diff --git a/.eslintrc.js b/.eslintrc.js
new file mode 100644
index 00000000..14721879
--- /dev/null
+++ b/.eslintrc.js
@@ -0,0 +1,20 @@
+/* eslint-env node */
+
+module.exports = {
+  plugins: [ 'metafizzy' ],
+  extends: 'plugin:metafizzy/browser',
+  env: {
+    browser: true,
+    commonjs: true,
+  },
+  parserOptions: {
+    ecmaVersion: 2018,
+  },
+  globals: {
+    InfiniteScroll: 'readonly',
+    QUnit: 'readonly',
+    define: 'readonly',
+  },
+  rules: {
+  },
+};
diff --git a/.nvmrc b/.nvmrc
new file mode 100644
index 00000000..8351c193
--- /dev/null
+++ b/.nvmrc
@@ -0,0 +1 @@
+14
diff --git a/gulpfile.js b/gulpfile.js
index 5377ae61..e716c358 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -1,55 +1,55 @@
-/*jshint node: true, strict: false */
+/* eslint-env node */
 
-var fs = require('fs');
-var gulp = require('gulp');
-var rename = require('gulp-rename');
-var replace = require('gulp-replace');
+let fs = require('fs');
+let gulp = require('gulp');
+let rename = require('gulp-rename');
+let replace = require('gulp-replace');
 
 // ----- hint ----- //
 
-var jshint = require('gulp-jshint');
+let jshint = require('gulp-jshint');
 
 gulp.task( 'hint-js', function() {
   return gulp.src('js/**/*.js')
     .pipe( jshint() )
     .pipe( jshint.reporter('default') );
-});
+} );
 
 gulp.task( 'hint-test', function() {
   return gulp.src('test/unit/*.js')
     .pipe( jshint() )
     .pipe( jshint.reporter('default') );
-});
+} );
 
 gulp.task( 'hint-task', function() {
   return gulp.src('gulpfile.js')
     .pipe( jshint() )
     .pipe( jshint.reporter('default') );
-});
+} );
 
-var jsonlint = require('gulp-json-lint');
+let jsonlint = require('gulp-json-lint');
 
 gulp.task( 'jsonlint', function() {
-  return gulp.src( '*.json' )
+  return gulp.src('*.json')
     .pipe( jsonlint() )
     .pipe( jsonlint.report('verbose') );
-});
+} );
 
-gulp.task( 'hint', [ 'hint-js', 'hint-test', 'hint-task', 'jsonlint' ]);
+gulp.task( 'hint', [ 'hint-js', 'hint-test', 'hint-task', 'jsonlint' ] );
 
 // -------------------------- RequireJS makes pkgd -------------------------- //
 
-var gutil = require('gulp-util');
-var chalk = require('chalk');
-var rjsOptimize = require('gulp-requirejs-optimize');
+let gutil = require('gulp-util');
+let chalk = require('chalk');
+let rjsOptimize = require('gulp-requirejs-optimize');
 
 // regex for banner comment
-var reBannerComment = new RegExp('^\\s*(?:\\/\\*[\\s\\S]*?\\*\\/)\\s*');
+let reBannerComment = new RegExp('^\\s*(?:\\/\\*[\\s\\S]*?\\*\\/)\\s*');
 
 function getBanner() {
-  var src = fs.readFileSync( 'js/index.js', 'utf8' );
-  var matches = src.match( reBannerComment );
-  var banner = matches[0].replace( 'Infinite Scroll', 'Infinite Scroll PACKAGED' );
+  let src = fs.readFileSync( 'js/index.js', 'utf8' );
+  let matches = src.match( reBannerComment );
+  let banner = matches[0].replace( 'Infinite Scroll', 'Infinite Scroll PACKAGED' );
   return banner;
 }
 
@@ -58,8 +58,8 @@ function addBanner( str ) {
 }
 
 gulp.task( 'requirejs', function() {
-  var banner = getBanner();
-  var definitionRE = /define\(\s*'infinite-scroll\/js\/index'(.|\n)+\],\s*factory/;
+  let banner = getBanner();
+  let definitionRE = /define\(\s*'infinite-scroll\/js\/index'(.|\n)+\],\s*factory/;
   // HACK src is not needed
   // should refactor rjsOptimize to produce src
   return gulp.src('js/index.js')
@@ -69,12 +69,12 @@ gulp.task( 'requirejs', function() {
       include: [
         'jquery-bridget/jquery-bridget',
         'infinite-scroll/js/index',
-        'imagesloaded/imagesloaded'
+        'imagesloaded/imagesloaded',
       ],
       paths: {
         'infinite-scroll': '../',
-        jquery: 'empty:'
-      }
+        jquery: 'empty:',
+      },
     }) )
     // munge AMD definition
     .pipe( replace( definitionRE, function( definition ) {
@@ -82,39 +82,38 @@ gulp.task( 'requirejs', function() {
       return definition.replace( "'infinite-scroll/js/index',", '' )
         // use explicit file paths, './history' -> 'infinite-scroll/js/history'
         .replace( /'.\//g, "'infinite-scroll/js/" );
-    }) )
+    } ) )
     // add banner
     .pipe( addBanner( banner ) )
     .pipe( rename('infinite-scroll.pkgd.js') )
     .pipe( gulp.dest('dist') );
-});
-
+} );
 
 // ----- uglify ----- //
 
-var uglify = require('gulp-uglify');
+let uglify = require('gulp-uglify');
 
 gulp.task( 'uglify', [ 'requirejs' ], function() {
-  var banner = getBanner();
+  let banner = getBanner();
   gulp.src('dist/infinite-scroll.pkgd.js')
     .pipe( uglify() )
     // add banner
     .pipe( addBanner( banner ) )
     .pipe( rename('infinite-scroll.pkgd.min.js') )
     .pipe( gulp.dest('dist') );
-});
+} );
 
 // ----- version ----- //
 
 // set version in source files
 
-var minimist = require('minimist');
+let minimist = require('minimist');
 
 // use gulp version -t 1.2.3
 gulp.task( 'version', function() {
-  var args = minimist( process.argv.slice(3) );
-  var version = args.t;
-  if ( !version || !/\d\.\d\.\d/.test( version ) ) {
+  let args = minimist( process.argv.slice( 3 ) );
+  let version = args.t;
+  if ( !version || !( /\d\.\d\.\d/ ).test( version ) ) {
     gutil.log( 'invalid version: ' + chalk.red( version ) );
     return;
   }
@@ -127,11 +126,11 @@ gulp.task( 'version', function() {
   gulp.src('package.json')
     .pipe( replace( /"version": "\d\.\d+\.\d+"/, '"version": "' + version + '"' ) )
     .pipe( gulp.dest('.') );
-});
+} );
 
 // ----- default ----- //
 
 gulp.task( 'default', [
   'hint',
   'uglify',
-]);
+] );
diff --git a/js/button.js b/js/button.js
index 106e398a..1b7042f1 100644
--- a/js/button.js
+++ b/js/button.js
@@ -1,7 +1,6 @@
 // button
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
@@ -9,20 +8,20 @@
       'fizzy-ui-utils/utils',
     ], function( InfiniteScroll, utils ) {
       return factory( window, InfiniteScroll, utils );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('./core'),
-      require('fizzy-ui-utils')
+        window,
+        require('./core'),
+        require('fizzy-ui-utils'),
     );
   } else {
     // browser global
     factory(
-      window,
-      window.InfiniteScroll,
-      window.fizzyUIUtils
+        window,
+        window.InfiniteScroll,
+        window.fizzyUIUtils,
     );
   }
 
@@ -31,10 +30,9 @@
 // InfiniteScroll.defaults.button = null;
 
 InfiniteScroll.create.button = function() {
-  var buttonElem = utils.getQueryElement( this.options.button );
+  let buttonElem = utils.getQueryElement( this.options.button );
   if ( buttonElem ) {
     this.button = new InfiniteScrollButton( buttonElem, this );
-    return;
   }
 };
 
@@ -85,4 +83,4 @@ InfiniteScroll.Button = InfiniteScrollButton;
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/js/core.js b/js/core.js
index 75c320a5..ddd1462c 100644
--- a/js/core.js
+++ b/js/core.js
@@ -1,39 +1,38 @@
 // core
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
       'ev-emitter/ev-emitter',
       'fizzy-ui-utils/utils',
-    ], function( EvEmitter, utils) {
+    ], function( EvEmitter, utils ) {
       return factory( window, EvEmitter, utils );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('ev-emitter'),
-      require('fizzy-ui-utils')
+        window,
+        require('ev-emitter'),
+        require('fizzy-ui-utils'),
     );
   } else {
     // browser global
     window.InfiniteScroll = factory(
-      window,
-      window.EvEmitter,
-      window.fizzyUIUtils
+        window,
+        window.EvEmitter,
+        window.fizzyUIUtils,
     );
   }
 
 }( window, function factory( window, EvEmitter, utils ) {
 
-var jQuery = window.jQuery;
+let jQuery = window.jQuery;
 // internal store of all InfiniteScroll intances
-var instances = {};
+let instances = {};
 
 function InfiniteScroll( element, options ) {
-  var queryElem = utils.getQueryElement( element );
+  let queryElem = utils.getQueryElement( element );
 
   if ( !queryElem ) {
     console.error( 'Bad element for InfiniteScroll: ' + ( queryElem || element ) );
@@ -42,7 +41,7 @@ function InfiniteScroll( element, options ) {
   element = queryElem;
   // do not initialize twice on same element
   if ( element.infiniteScrollGUID ) {
-    var instance = instances[ element.infiniteScrollGUID ];
+    let instance = instances[ element.infiniteScrollGUID ];
     instance.option( options );
     return instance;
   }
@@ -70,19 +69,19 @@ InfiniteScroll.defaults = {
 InfiniteScroll.create = {};
 InfiniteScroll.destroy = {};
 
-var proto = InfiniteScroll.prototype;
+let proto = InfiniteScroll.prototype;
 // inherit EvEmitter
 utils.extend( proto, EvEmitter.prototype );
 
 // --------------------------  -------------------------- //
 
 // globally unique identifiers
-var GUID = 0;
+let GUID = 0;
 
 proto.create = function() {
   // create core
   // add id for InfiniteScroll.data
-  var id = this.guid = ++GUID;
+  let id = this.guid = ++GUID;
   this.element.infiniteScrollGUID = id; // expando
   instances[ id ] = this; // associate via id
   // properties
@@ -90,7 +89,7 @@ proto.create = function() {
   this.loadCount = 0;
   this.updateGetPath();
   // bail if getPath not set, or returns falsey #776
-  var hasPath = this.getPath && this.getPath();
+  let hasPath = this.getPath && this.getPath();
   if ( !hasPath ) {
     console.error('Disabling InfiniteScroll');
     return;
@@ -99,7 +98,7 @@ proto.create = function() {
   this.log( 'initialized', [ this.element.className ] );
   this.callOnInit();
   // create features
-  for ( var method in InfiniteScroll.create ) {
+  for ( let method in InfiniteScroll.create ) {
     InfiniteScroll.create[ method ].call( this );
   }
 };
@@ -110,7 +109,7 @@ proto.option = function( opts ) {
 
 // call onInit option, used for binding events on init
 proto.callOnInit = function() {
-  var onInit = this.options.onInit;
+  let onInit = this.options.onInit;
   if ( onInit ) {
     onInit.call( this, this );
   }
@@ -120,7 +119,7 @@ proto.callOnInit = function() {
 
 proto.dispatchEvent = function( type, event, args ) {
   this.log( type, args );
-  var emitArgs = event ? [ event ].concat( args ) : args;
+  let emitArgs = event ? [ event ].concat( args ) : args;
   this.emitEvent( type, emitArgs );
   // trigger jQuery event
   if ( !jQuery || !this.$element ) {
@@ -128,17 +127,18 @@ proto.dispatchEvent = function( type, event, args ) {
   }
   // namespace jQuery event
   type += '.infiniteScroll';
-  var $event = type;
+  let $event = type;
   if ( event ) {
     // create jQuery event
-    var jQEvent = jQuery.Event( event );
+    /* eslint-disable-next-line new-cap */
+    let jQEvent = jQuery.Event( event );
     jQEvent.type = type;
     $event = jQEvent;
   }
   this.$element.trigger( $event, args );
 };
 
-var loggers = {
+let loggers = {
   initialized: function( className ) {
     return 'on ' + className;
   },
@@ -170,8 +170,8 @@ proto.log = function( type, args ) {
   if ( !this.options.debug ) {
     return;
   }
-  var message = '[InfiniteScroll] ' + type;
-  var logger = loggers[ type ];
+  let message = '[InfiniteScroll] ' + type;
+  let logger = loggers[ type ];
   if ( logger ) {
     message += '. ' + logger.apply( this, args );
   }
@@ -182,12 +182,12 @@ proto.log = function( type, args ) {
 
 proto.updateMeasurements = function() {
   this.windowHeight = window.innerHeight;
-  var rect = this.element.getBoundingClientRect();
+  let rect = this.element.getBoundingClientRect();
   this.top = rect.top + window.pageYOffset;
 };
 
 proto.updateScroller = function() {
-  var elementScroll = this.options.elementScroll;
+  let elementScroll = this.options.elementScroll;
   if ( !elementScroll ) {
     // default, use window
     this.scroller = window;
@@ -197,26 +197,26 @@ proto.updateScroller = function() {
   this.scroller = elementScroll === true ? this.element :
     utils.getQueryElement( elementScroll );
   if ( !this.scroller ) {
-    throw 'Unable to find elementScroll: ' + elementScroll;
+    throw new Error( 'Unable to find elementScroll: ' + elementScroll );
   }
 };
 
 // -------------------------- page path -------------------------- //
 
 proto.updateGetPath = function() {
-  var optPath = this.options.path;
+  let optPath = this.options.path;
   if ( !optPath ) {
     console.error( 'InfiniteScroll path option required. Set as: ' + optPath );
     return;
   }
   // function
-  var type = typeof optPath;
+  let type = typeof optPath;
   if ( type == 'function' ) {
     this.getPath = optPath;
     return;
   }
   // template string: '/pages/{{#}}.html'
-  var templateMatch = type == 'string' && optPath.match('{{#}}');
+  let templateMatch = type == 'string' && optPath.match('{{#}}');
   if ( templateMatch ) {
     this.updateGetPathTemplate( optPath );
     return;
@@ -228,17 +228,17 @@ proto.updateGetPath = function() {
 proto.updateGetPathTemplate = function( optPath ) {
   // set getPath with template string
   this.getPath = function() {
-    var nextIndex = this.pageIndex + 1;
+    let nextIndex = this.pageIndex + 1;
     return optPath.replace( '{{#}}', nextIndex );
   }.bind( this );
   // get pageIndex from location
   // convert path option into regex to look for pattern in location
-  // escape query (?) in url, allows for parsing GET parameters 
-  var regexString = optPath
+  // escape query (?) in url, allows for parsing GET parameters
+  let regexString = optPath
     .replace( /(\\\?|\?)/, '\\?' )
     .replace( '{{#}}', '(\\d\\d?\\d?)' );
-  var templateRe = new RegExp( regexString );
-  var match = location.href.match( templateRe );
+  let templateRe = new RegExp( regexString );
+  let match = location.href.match( templateRe );
 
   if ( match ) {
     this.pageIndex = parseInt( match[1], 10 );
@@ -246,7 +246,7 @@ proto.updateGetPathTemplate = function( optPath ) {
   }
 };
 
-var pathRegexes = [
+let pathRegexes = [
   // WordPress & Tumblr - example.com/page/2
   // Jekyll - example.com/page2
   /^(.*?\/?page\/?)(\d\d?\d?)(.*?$)/,
@@ -258,21 +258,23 @@ var pathRegexes = [
 
 proto.updateGetPathSelector = function( optPath ) {
   // parse href of link: '.next-page-link'
-  var hrefElem = document.querySelector( optPath );
+  let hrefElem = document.querySelector( optPath );
   if ( !hrefElem ) {
     console.error( 'Bad InfiniteScroll path option. Next link not found: ' +
       optPath );
     return;
   }
-  var href = hrefElem.getAttribute('href');
+  let href = hrefElem.getAttribute('href');
   // try matching href to pathRegexes patterns
-  var pathParts, regex;
-  for ( var i=0; href && i < pathRegexes.length; i++ ) {
-    regex = pathRegexes[i];
-    var match = href.match( regex );
-    if ( match ) {
-      pathParts = match.slice(1); // remove first part
-      break;
+  let pathParts, regex;
+  if ( href ) {
+    for ( let i = 0; i < pathRegexes.length; i++ ) {
+      regex = pathRegexes[i];
+      let match = href.match( regex );
+      if ( match ) {
+        pathParts = match.slice( 1 ); // remove first part
+        break;
+      }
     }
   }
   if ( !pathParts ) {
@@ -281,7 +283,7 @@ proto.updateGetPathSelector = function( optPath ) {
   }
   this.isPathSelector = true; // flag for checkLastPage()
   this.getPath = function() {
-    var nextIndex = this.pageIndex + 1;
+    let nextIndex = this.pageIndex + 1;
     return pathParts[0] + nextIndex + pathParts[2];
   }.bind( this );
   // get pageIndex from href
@@ -290,17 +292,17 @@ proto.updateGetPathSelector = function( optPath ) {
 };
 
 proto.updateGetAbsolutePath = function() {
-  var path = this.getPath();
+  let path = this.getPath();
   // path doesn't start with http or /
-  var isAbsolute = path.match( /^http/ ) || path.match( /^\// );
+  let isAbsolute = path.match( /^http/ ) || path.match( /^\// );
   if ( isAbsolute ) {
     this.getAbsolutePath = this.getPath;
     return;
   }
 
-  var pathname = location.pathname;
+  let pathname = location.pathname;
   // query parameter #829. example.com/?pg=2
-  var isQuery = path.match( /^\?/ );
+  let isQuery = path.match( /^\?/ );
   if ( isQuery ) {
     this.getAbsolutePath = function() {
       return pathname + this.getPath();
@@ -309,7 +311,7 @@ proto.updateGetAbsolutePath = function() {
   }
 
   // /foo/bar/index.html => /foo/bar
-  var directory = pathname.substring( 0, pathname.lastIndexOf('/') );
+  let directory = pathname.substring( 0, pathname.lastIndexOf('/') );
   this.getAbsolutePath = function() {
     return directory + '/' + this.getPath();
   };
@@ -319,7 +321,7 @@ proto.updateGetAbsolutePath = function() {
 
 // hide navigation
 InfiniteScroll.create.hideNav = function() {
-  var nav = utils.getQueryElement( this.options.hideNav );
+  let nav = utils.getQueryElement( this.options.hideNav );
   if ( !nav ) {
     return;
   }
@@ -338,7 +340,7 @@ InfiniteScroll.destroy.hideNav = function() {
 proto.destroy = function() {
   this.allOff(); // remove all event listeners
   // call destroy methods
-  for ( var method in InfiniteScroll.destroy ) {
+  for ( let method in InfiniteScroll.destroy ) {
     InfiniteScroll.destroy[ method ].call( this );
   }
 
@@ -355,12 +357,12 @@ proto.destroy = function() {
 // https://remysharp.com/2010/07/21/throttling-function-calls
 InfiniteScroll.throttle = function( fn, threshold ) {
   threshold = threshold || 200;
-  var last, timeout;
+  let last, timeout;
 
   return function() {
-    var now = +new Date();
-    var args = arguments;
-    var trigger = function() {
+    let now = +new Date();
+    let args = arguments;
+    let trigger = function() {
       last = now;
       fn.apply( this, args );
     }.bind( this );
@@ -376,13 +378,13 @@ InfiniteScroll.throttle = function( fn, threshold ) {
 
 InfiniteScroll.data = function( elem ) {
   elem = utils.getQueryElement( elem );
-  var id = elem && elem.infiniteScrollGUID;
+  let id = elem && elem.infiniteScrollGUID;
   return id && instances[ id ];
 };
 
 // set internal jQuery, for Webpack + jQuery v3
-InfiniteScroll.setJQuery = function( $ ) {
-  jQuery = $;
+InfiniteScroll.setJQuery = function( jqry ) {
+  jQuery = jqry;
 };
 
 // -------------------------- setup -------------------------- //
@@ -400,4 +402,4 @@ if ( jQuery && jQuery.bridget ) {
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/js/history.js b/js/history.js
index 8525d07e..903097f8 100644
--- a/js/history.js
+++ b/js/history.js
@@ -1,7 +1,6 @@
 // history
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
@@ -9,31 +8,31 @@
       'fizzy-ui-utils/utils',
     ], function( InfiniteScroll, utils ) {
       return factory( window, InfiniteScroll, utils );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('./core'),
-      require('fizzy-ui-utils')
+        window,
+        require('./core'),
+        require('fizzy-ui-utils'),
     );
   } else {
     // browser global
     factory(
-      window,
-      window.InfiniteScroll,
-      window.fizzyUIUtils
+        window,
+        window.InfiniteScroll,
+        window.fizzyUIUtils,
     );
   }
 
 }( window, function factory( window, InfiniteScroll, utils ) {
 
-var proto = InfiniteScroll.prototype;
+let proto = InfiniteScroll.prototype;
 
 InfiniteScroll.defaults.history = 'replace';
 // InfiniteScroll.defaults.historyTitle = false;
 
-var link = document.createElement('a');
+let link = document.createElement('a');
 
 // ----- create/destroy ----- //
 
@@ -43,9 +42,10 @@ InfiniteScroll.create.history = function() {
   }
   // check for same origin
   link.href = this.getAbsolutePath();
-  // MS Edge does not have origin on link https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12236493/
-  var linkOrigin = link.origin || link.protocol + '//' + link.host;
-  var isSameOrigin = linkOrigin == location.origin;
+  // MS Edge does not have origin on link
+  // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12236493/
+  let linkOrigin = link.origin || link.protocol + '//' + link.host;
+  let isSameOrigin = linkOrigin == location.origin;
   if ( !isSameOrigin ) {
     console.error( '[InfiniteScroll] cannot set history with different origin: ' +
       link.origin + ' on ' + location.origin +
@@ -71,7 +71,7 @@ proto.createHistoryAppend = function() {
       top: 0,
       path: location.href,
       title: document.title,
-    }
+    },
   ];
   this.scrollPageIndex = 0;
   // events
@@ -83,7 +83,7 @@ proto.createHistoryAppend = function() {
 };
 
 proto.bindHistoryAppendEvents = function( isBind ) {
-  var addRemove = isBind ? 'addEventListener' : 'removeEventListener';
+  let addRemove = isBind ? 'addEventListener' : 'removeEventListener';
   this.scroller[ addRemove ]( 'scroll', this.scrollHistoryHandler );
   window[ addRemove ]( 'unload', this.unloadHandler );
 };
@@ -94,7 +94,7 @@ proto.createHistoryPageLoad = function() {
 
 InfiniteScroll.destroy.history =
 proto.destroyHistory = function() {
-  var isHistoryAppend = this.options.history && this.options.append;
+  let isHistoryAppend = this.options.history && this.options.append;
   if ( isHistoryAppend ) {
     this.bindHistoryAppendEvents( false );
   }
@@ -107,8 +107,8 @@ proto.onAppendHistory = function( response, path, items ) {
   if ( !items || !items.length ) {
     return;
   }
-  var firstItem = items[0];
-  var elemScrollY = this.getElementScrollY( firstItem );
+  let firstItem = items[0];
+  let elemScrollY = this.getElementScrollY( firstItem );
   // resolve path
   link.href = path;
   // add page data to hash
@@ -128,7 +128,7 @@ proto.getElementScrollY = function( elem ) {
 };
 
 proto.getElementWindowScrollY = function( elem ) {
-  var rect = elem.getBoundingClientRect();
+  let rect = elem.getBoundingClientRect();
   return rect.top + window.pageYOffset;
 };
 
@@ -139,10 +139,10 @@ proto.getElementElementScrollY = function( elem ) {
 
 proto.onScrollHistory = function() {
   // cycle through positions, find biggest without going over
-  var scrollViewY = this.getScrollViewY();
-  var pageIndex, page;
-  for ( var i=0; i < this.scrollPages.length; i++ ) {
-    var scrollPage = this.scrollPages[i];
+  let scrollViewY = this.getScrollViewY();
+  let pageIndex, page;
+  for ( let i = 0; i < this.scrollPages.length; i++ ) {
+    let scrollPage = this.scrollPages[i];
     if ( scrollPage.top >= scrollViewY ) {
       break;
     }
@@ -160,15 +160,15 @@ utils.debounceMethod( InfiniteScroll, 'onScrollHistory', 150 );
 
 proto.getScrollViewY = function() {
   if ( this.options.elementScroll ) {
-    return this.scroller.scrollTop + this.scroller.clientHeight/2;
+    return this.scroller.scrollTop + this.scroller.clientHeight / 2;
   } else {
-    return window.pageYOffset + this.windowHeight/2;
+    return window.pageYOffset + this.windowHeight / 2;
   }
 };
 
 proto.setHistory = function( title, path ) {
-  var optHistory = this.options.history;
-  var historyMethod = optHistory && history[ optHistory + 'State' ];
+  let optHistory = this.options.history;
+  let historyMethod = optHistory && history[ optHistory + 'State' ];
   if ( !historyMethod ) {
     return;
   }
@@ -185,13 +185,13 @@ proto.setHistory = function( title, path ) {
 // scroll to top to prevent initial scroll-reset after page refresh
 // https://stackoverflow.com/a/18633915/182183
 proto.onUnload = function() {
-  var pageIndex = this.scrollPageIndex;
+  let pageIndex = this.scrollPageIndex;
   if ( pageIndex === 0 ) {
     return;
   }
   // calculate where scroll position would be on refresh
-  var scrollPage = this.scrollPages[ pageIndex ];
-  var scrollY = window.pageYOffset - scrollPage.top + this.top;
+  let scrollPage = this.scrollPages[ pageIndex ];
+  let scrollY = window.pageYOffset - scrollPage.top + this.top;
   // disable scroll event before setting scroll #679
   this.destroyHistory();
   scrollTo( 0, scrollY );
@@ -208,4 +208,4 @@ proto.onPageLoadHistory = function( response, path ) {
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/js/index.js b/js/index.js
index b010a736..5024526e 100644
--- a/js/index.js
+++ b/js/index.js
@@ -11,7 +11,6 @@
 
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
@@ -25,15 +24,15 @@
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      require('./core'),
-      require('./page-load'),
-      require('./scroll-watch'),
-      require('./history'),
-      require('./button'),
-      require('./status')
+        require('./core'),
+        require('./page-load'),
+        require('./scroll-watch'),
+        require('./history'),
+        require('./button'),
+        require('./status'),
     );
   }
 
-})( window, function factory( InfiniteScroll ) {
+} )( window, function factory( InfiniteScroll ) {
   return InfiniteScroll;
-});
+} );
diff --git a/js/page-load.js b/js/page-load.js
index b3fc6ada..11d34668 100644
--- a/js/page-load.js
+++ b/js/page-load.js
@@ -1,31 +1,30 @@
 // page-load
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
       './core',
     ], function( InfiniteScroll ) {
       return factory( window, InfiniteScroll );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('./core')
+        window,
+        require('./core'),
     );
   } else {
     // browser global
     factory(
-      window,
-      window.InfiniteScroll
+        window,
+        window.InfiniteScroll,
     );
   }
 
 }( window, function factory( window, InfiniteScroll ) {
 
-var proto = InfiniteScroll.prototype;
+let proto = InfiniteScroll.prototype;
 
 // InfiniteScroll.defaults.append = false;
 InfiniteScroll.defaults.loadOnScroll = true;
@@ -54,18 +53,18 @@ proto.loadNextPage = function() {
     return;
   }
 
-  var path = this.getAbsolutePath();
+  let path = this.getAbsolutePath();
   this.isLoading = true;
 
-  var onLoad = function( response ) {
+  let onLoad = function( response ) {
     this.onPageLoad( response, path );
   }.bind( this );
 
-  var onError = function( error ) {
+  let onError = function( error ) {
     this.onPageError( error, path );
   }.bind( this );
 
-  var onLast = function( response ) {
+  let onLast = function( response ) {
     this.lastPageReached( response, path );
   }.bind( this );
 
@@ -86,16 +85,16 @@ proto.onPageLoad = function( response, path ) {
 };
 
 proto.appendNextPage = function( response, path ) {
-  var optAppend = this.options.append;
+  let optAppend = this.options.append;
   // do not append json
-  var isDocument = this.options.responseType == 'document';
+  let isDocument = this.options.responseType == 'document';
   if ( !isDocument || !optAppend ) {
     return;
   }
 
-  var items = response.querySelectorAll( optAppend );
-  var fragment = getItemsFragment( items );
-  var appendReady = function () {
+  let items = response.querySelectorAll( optAppend );
+  let fragment = getItemsFragment( items );
+  let appendReady = function() {
     this.appendItems( items, fragment );
     this.isLoading = false;
     this.dispatchEvent( 'append', null, [ response, path, items ] );
@@ -121,9 +120,11 @@ proto.appendItems = function( items, fragment ) {
 
 function getItemsFragment( items ) {
   // add items to fragment
-  var fragment = document.createDocumentFragment();
-  for ( var i=0; items && i < items.length; i++ ) {
-    fragment.appendChild( items[i] );
+  let fragment = document.createDocumentFragment();
+  if ( items ) {
+    for ( let i = 0; i < items.length; i++ ) {
+      fragment.appendChild( items[i] );
+    }
   }
   return fragment;
 }
@@ -132,10 +133,10 @@ function getItemsFragment( items ) {
 // <script>s added by InfiniteScroll will not load
 // similar to https://stackoverflow.com/questions/610995
 function refreshScripts( fragment ) {
-  var scripts = fragment.querySelectorAll('script');
-  for ( var i=0; i < scripts.length; i++ ) {
-    var script = scripts[i];
-    var freshScript = document.createElement('script');
+  let scripts = fragment.querySelectorAll('script');
+  for ( let i = 0; i < scripts.length; i++ ) {
+    let script = scripts[i];
+    let freshScript = document.createElement('script');
     copyAttributes( script, freshScript );
     // copy inner script code. #718, #782
     freshScript.innerHTML = script.innerHTML;
@@ -144,9 +145,9 @@ function refreshScripts( fragment ) {
 }
 
 function copyAttributes( fromNode, toNode ) {
-  var attrs = fromNode.attributes;
-  for ( var i=0; i < attrs.length; i++ ) {
-    var attr = attrs[i];
+  let attrs = fromNode.attributes;
+  for ( let i = 0; i < attrs.length; i++ ) {
+    let attr = attrs[i];
     toNode.setAttribute( attr.name, attr.value );
   }
 }
@@ -154,7 +155,7 @@ function copyAttributes( fromNode, toNode ) {
 // ----- outlayer ----- //
 
 proto.appendOutlayerItems = function( fragment, appendReady ) {
-  var imagesLoaded = InfiniteScroll.imagesLoaded || window.imagesLoaded;
+  let imagesLoaded = InfiniteScroll.imagesLoaded || window.imagesLoaded;
   if ( !imagesLoaded ) {
     console.error('[InfiniteScroll] imagesLoaded required for outlayer option');
     this.isLoading = false;
@@ -172,22 +173,22 @@ proto.onAppendOutlayer = function( response, path, items ) {
 
 // check response for next element
 proto.checkLastPage = function( response, path ) {
-  var checkLastPage = this.options.checkLastPage;
+  let checkLastPage = this.options.checkLastPage;
   if ( !checkLastPage ) {
     return;
   }
 
-  var pathOpt = this.options.path;
+  let pathOpt = this.options.path;
   // if path is function, check if next path is truthy
   if ( typeof pathOpt == 'function' ) {
-    var nextPath = this.getPath();
+    let nextPath = this.getPath();
     if ( !nextPath ) {
       this.lastPageReached( response, path );
       return;
     }
   }
   // get selector from checkLastPage or path option
-  var selector;
+  let selector;
   if ( typeof checkLastPage == 'string' ) {
     selector = checkLastPage;
   } else if ( this.isPathSelector ) {
@@ -200,7 +201,7 @@ proto.checkLastPage = function( response, path ) {
     return;
   }
   // check if response has selector
-  var nextElem = response.querySelector( selector );
+  let nextElem = response.querySelector( selector );
   if ( !nextElem ) {
     this.lastPageReached( response, path );
   }
@@ -226,7 +227,7 @@ InfiniteScroll.create.prefill = function() {
   if ( !this.options.prefill ) {
     return;
   }
-  var append = this.options.append;
+  let append = this.options.append;
   if ( !append ) {
     console.error( 'append option required for prefill. Set as :' + append );
     return;
@@ -241,7 +242,7 @@ InfiniteScroll.create.prefill = function() {
 };
 
 proto.prefill = function() {
-  var distance = this.getPrefillDistance();
+  let distance = this.getPrefillDistance();
   this.isPrefilling = distance >= 0;
   if ( this.isPrefilling ) {
     this.log('prefill');
@@ -267,14 +268,15 @@ proto.stopPrefill = function() {
 
 // -------------------------- request -------------------------- //
 
+/* eslint-disable-next-line max-params */
 function request( url, responseType, onLoad, onError, onLast ) {
-  var req = new XMLHttpRequest();
+  let req = new XMLHttpRequest();
   req.open( 'GET', url, true );
   // set responseType document to return DOM
   req.responseType = responseType || '';
 
   // set X-Requested-With header to check that is ajax request
-  req.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
+  req.setRequestHeader( 'X-Requested-With', 'XMLHttpRequest' );
 
   req.onload = function() {
     if ( req.status == 200 ) {
@@ -283,14 +285,14 @@ function request( url, responseType, onLoad, onError, onLast ) {
       onLast( req.response );
     } else {
       // not 200 OK, error
-      var error = new Error( req.statusText );
+      let error = new Error( req.statusText );
       onError( error );
     }
   };
 
   // Handle network errors
   req.onerror = function() {
-    var error = new Error( 'Network error requesting ' + url );
+    let error = new Error( 'Network error requesting ' + url );
     onError( error );
   };
 
@@ -301,4 +303,4 @@ function request( url, responseType, onLoad, onError, onLast ) {
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/js/scroll-watch.js b/js/scroll-watch.js
index e832889e..cfc012ba 100644
--- a/js/scroll-watch.js
+++ b/js/scroll-watch.js
@@ -1,7 +1,6 @@
 // scroll-watch
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
@@ -9,26 +8,26 @@
       'fizzy-ui-utils/utils',
     ], function( InfiniteScroll, utils ) {
       return factory( window, InfiniteScroll, utils );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('./core'),
-      require('fizzy-ui-utils')
+        window,
+        require('./core'),
+        require('fizzy-ui-utils'),
     );
   } else {
     // browser global
     factory(
-      window,
-      window.InfiniteScroll,
-      window.fizzyUIUtils
+        window,
+        window.InfiniteScroll,
+        window.fizzyUIUtils,
     );
   }
 
 }( window, function factory( window, InfiniteScroll, utils ) {
 
-var proto = InfiniteScroll.prototype;
+let proto = InfiniteScroll.prototype;
 
 // default options
 InfiniteScroll.defaults.scrollThreshold = 400;
@@ -39,8 +38,8 @@ InfiniteScroll.create.scrollWatch = function() {
   this.pageScrollHandler = this.onPageScroll.bind( this );
   this.resizeHandler = this.onResize.bind( this );
 
-  var scrollThreshold = this.options.scrollThreshold;
-  var isEnable = scrollThreshold || scrollThreshold === 0;
+  let scrollThreshold = this.options.scrollThreshold;
+  let isEnable = scrollThreshold || scrollThreshold === 0;
   if ( isEnable ) {
     this.enableScrollWatch();
   }
@@ -71,17 +70,17 @@ proto.disableScrollWatch = function() {
 };
 
 proto.bindScrollWatchEvents = function( isBind ) {
-  var addRemove = isBind ? 'addEventListener' : 'removeEventListener';
+  let addRemove = isBind ? 'addEventListener' : 'removeEventListener';
   this.scroller[ addRemove ]( 'scroll', this.pageScrollHandler );
   window[ addRemove ]( 'resize', this.resizeHandler );
 };
 
 proto.onPageScroll = InfiniteScroll.throttle( function() {
-  var distance = this.getBottomDistance();
+  let distance = this.getBottomDistance();
   if ( distance <= this.options.scrollThreshold ) {
     this.dispatchEvent('scrollThreshold');
   }
-});
+} );
 
 proto.getBottomDistance = function() {
   if ( this.options.elementScroll ) {
@@ -92,14 +91,14 @@ proto.getBottomDistance = function() {
 };
 
 proto.getWindowBottomDistance = function() {
-  var bottom = this.top + this.element.clientHeight;
-  var scrollY = window.pageYOffset + this.windowHeight;
+  let bottom = this.top + this.element.clientHeight;
+  let scrollY = window.pageYOffset + this.windowHeight;
   return bottom - scrollY;
 };
 
 proto.getElementBottomDistance = function() {
-  var bottom = this.scroller.scrollHeight;
-  var scrollY = this.scroller.scrollTop + this.scroller.clientHeight;
+  let bottom = this.scroller.scrollHeight;
+  let scrollY = this.scroller.scrollTop + this.scroller.clientHeight;
   return bottom - scrollY;
 };
 
@@ -113,4 +112,4 @@ utils.debounceMethod( InfiniteScroll, 'onResize', 150 );
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/js/status.js b/js/status.js
index bdb4044d..ab8ebf8f 100644
--- a/js/status.js
+++ b/js/status.js
@@ -1,7 +1,6 @@
 // status
 ( function( window, factory ) {
   // universal module definition
-  /* globals define, module, require */
   if ( typeof define == 'function' && define.amd ) {
     // AMD
     define( [
@@ -9,31 +8,31 @@
       'fizzy-ui-utils/utils',
     ], function( InfiniteScroll, utils ) {
       return factory( window, InfiniteScroll, utils );
-    });
+    } );
   } else if ( typeof module == 'object' && module.exports ) {
     // CommonJS
     module.exports = factory(
-      window,
-      require('./core'),
-      require('fizzy-ui-utils')
+        window,
+        require('./core'),
+        require('fizzy-ui-utils'),
     );
   } else {
     // browser global
     factory(
-      window,
-      window.InfiniteScroll,
-      window.fizzyUIUtils
+        window,
+        window.InfiniteScroll,
+        window.fizzyUIUtils,
     );
   }
 
-}( window, function factory( window, InfiniteScroll, utils ) { 
+}( window, function factory( window, InfiniteScroll, utils ) {
 
-var proto = InfiniteScroll.prototype;
+let proto = InfiniteScroll.prototype;
 
 // InfiniteScroll.defaults.status = null;
 
 InfiniteScroll.create.status = function() {
-  var statusElem = utils.getQueryElement( this.options.status );
+  let statusElem = utils.getQueryElement( this.options.status );
   if ( !statusElem ) {
     return;
   }
@@ -52,7 +51,7 @@ InfiniteScroll.create.status = function() {
 };
 
 proto.bindHideStatus = function( bindMethod ) {
-  var hideEvent = this.options.append ? 'append' : 'load';
+  let hideEvent = this.options.append ? 'append' : 'load';
   this[ bindMethod ]( hideEvent, this.hideAllStatus );
 };
 
@@ -73,7 +72,7 @@ proto.showLastStatus = function() {
 proto.showStatus = function( eventName ) {
   show( this.statusElement );
   this.hideStatusEventElements();
-  var eventElem = this.statusEventElements[ eventName ];
+  let eventElem = this.statusEventElements[ eventName ];
   show( eventElem );
 };
 
@@ -83,8 +82,8 @@ proto.hideAllStatus = function() {
 };
 
 proto.hideStatusEventElements = function() {
-  for ( var type in this.statusEventElements ) {
-    var eventElem = this.statusEventElements[ type ];
+  for ( let type in this.statusEventElements ) {
+    let eventElem = this.statusEventElements[ type ];
     hide( eventElem );
   }
 };
@@ -109,4 +108,4 @@ function setDisplay( elem, value ) {
 
 return InfiniteScroll;
 
-}));
+} ) );
diff --git a/package.json b/package.json
index 36d3effc..2e5fe589 100644
--- a/package.json
+++ b/package.json
@@ -13,6 +13,8 @@
   },
   "devDependencies": {
     "chalk": "^0.5.1",
+    "eslint": "^7.15.0",
+    "eslint-plugin-metafizzy": "^1.1.1",
     "gulp": "^3.9.1",
     "gulp-jshint": "^1.12.0",
     "gulp-json-lint": "0.0.1",
@@ -29,6 +31,7 @@
     "qunitjs": "^2.3.2"
   },
   "scripts": {
+    "lint": "npx eslint .",
     "test": "echo \"View test/ in browser\" && exit 1"
   },
   "repository": {
diff --git a/sandbox/js/masonry-images.js b/sandbox/js/masonry-images.js
index 45af3591..63fa7a97 100644
--- a/sandbox/js/masonry-images.js
+++ b/sandbox/js/masonry-images.js
@@ -1,5 +1,5 @@
-
-var msnry = new Masonry( '.grid', {
+/* globals Masonry, imagesLoaded */
+let msnry = new Masonry( '.grid', {
   itemSelector: 'none', // select no images on init
   columnWidth: '.grid__col-sizer',
   gutter: '.grid__gutter-sizer',
@@ -7,26 +7,26 @@ var msnry = new Masonry( '.grid', {
   stagger: 30,
   visibleStyle: {
     transform: 'translateY(0)',
-    opacity: 1
+    opacity: 1,
   },
   hiddenStyle: {
     transform: 'translateY(100px)',
     opacity: 0,
-  }
-});
+  },
+} );
 
 imagesLoaded( '.grid', function() {
   msnry.options.itemSelector = '.grid__item'; // select proper items
   document.querySelector('.grid').classList.add('are-images-ready');
-  var items = document.querySelectorAll('.grid__item');
+  let items = document.querySelectorAll('.grid__item');
   msnry.appended( items );
-});
+} );
 
-var infScroll = new InfiniteScroll( '.grid', {
+window.infScroll = new InfiniteScroll( '.grid', {
   path: '.pagination__next',
   append: '.grid__item',
   debug: true,
   outlayer: msnry,
   status: '.scroll-status',
   scrollThreshold: 1,
-});
+} );
diff --git a/sandbox/js/scroll-loader.js b/sandbox/js/scroll-loader.js
index da0d2eb8..b07e4791 100644
--- a/sandbox/js/scroll-loader.js
+++ b/sandbox/js/scroll-loader.js
@@ -1,9 +1,9 @@
-var container = document.querySelector('.posts-container');
-var infScroll = new InfiniteScroll( container, {
+let container = document.querySelector('.posts-container');
+window.infScroll = new InfiniteScroll( container, {
   path: '.pagination__next',
   append: '.post',
   nav: '.pagination',
   status: '.scroll-status',
   debug: true,
   // history: false,
-});
+} );
diff --git a/sandbox/js/unsplash.js b/sandbox/js/unsplash.js
index 3e683942..49d1e3d3 100644
--- a/sandbox/js/unsplash.js
+++ b/sandbox/js/unsplash.js
@@ -1,20 +1,20 @@
-var container = document.querySelector('.container');
+let container = document.querySelector('.container');
 
-var unsplashID = '9ad80b14098bcead9c7de952435e937cc3723ae61084ba8e729adb642daf0251';
+let unsplashID = '9ad80b14098bcead9c7de952435e937cc3723ae61084ba8e729adb642daf0251';
 
-var infScroll = new InfiniteScroll( '.container', {
+let infScroll = new InfiniteScroll( '.container', {
   path: 'https://api.unsplash.com/photos?page={{#}}&client_id=' + unsplashID,
   responseType: '',
   history: false,
-});
+} );
 
 infScroll.on( 'load', function( response ) {
-  var data = JSON.parse( response );
-  var itemsHTML = data.map( getItem ).join('');
+  let data = JSON.parse( response );
+  let itemsHTML = data.map( getItem ).join('');
   container.innerHTML += itemsHTML;
-});
+} );
 
-var itemTemplateSrc = document.querySelector('#item-template').innerHTML;
+let itemTemplateSrc = document.querySelector('#item-template').innerHTML;
 
 function getItem( photo ) {
   return microTemplate( itemTemplateSrc, photo );
@@ -23,14 +23,14 @@ function getItem( photo ) {
 // micro templating, sort-of
 function microTemplate( src, data ) {
   // replace {{tags}} in source
-  return src.replace( /\{\{([\w\-_\.]+)\}\}/gi, function( match, key ) {
+  return src.replace( /\{\{([\w\-_.]+)\}\}/gi, function( match, key ) {
     // walk through objects to get value
-    var value = data;
+    let value = data;
     key.split('.').forEach( function( part ) {
       value = value[ part ];
-    });
+    } );
     return value;
-  });
+  } );
 }
 
 // load first page
diff --git a/sandbox/requirejs/requirejs-main.js b/sandbox/requirejs/requirejs-main.js
index c7ae3918..723afcbf 100644
--- a/sandbox/requirejs/requirejs-main.js
+++ b/sandbox/requirejs/requirejs-main.js
@@ -1,4 +1,4 @@
-/*global requirejs: false*/
+/* global requirejs: false*/
 
 // ---- bower components ---- //
 
@@ -11,7 +11,7 @@
 // ---- pkgd ---- //
 
 requirejs( [
-  '../../dist/infinite-scroll.pkgd.js'
+  '../../dist/infinite-scroll.pkgd.js',
 ], initScroll );
 
 function initScroll( InfiniteScroll ) {
@@ -22,5 +22,5 @@ function initScroll( InfiniteScroll ) {
     status: '.scroll-status',
     debug: true,
     history: false,
-  });
+  } );
 }
diff --git a/test/unit/check-last-page.js b/test/unit/check-last-page.js
index aa2beb83..ea6c0b54 100644
--- a/test/unit/check-last-page.js
+++ b/test/unit/check-last-page.js
@@ -1,15 +1,15 @@
 QUnit.test( 'checkLastPage', function( assert ) {
 
-  var done = assert.async();
+  let done = assert.async();
 
   // ----- checkLastPage: true ----- //
 
-  var infScroll = new InfiniteScroll( '.demo--check-last-page', {
+  let infScroll = new InfiniteScroll( '.demo--check-last-page', {
     path: '.check-last-page-next-link',
     append: '.post',
     scrollThreshold: false,
     history: false,
-  });
+  } );
 
   infScroll.on( 'last', onTrueLast1 );
   infScroll.once( 'append', onTrueAppend1 );
@@ -29,7 +29,7 @@ QUnit.test( 'checkLastPage', function( assert ) {
     infScroll.once( 'last', function() {
       assert.ok( true, 'checkLastPage: true, last triggered on 3rd page' );
       checkString();
-    });
+    } );
 
     infScroll.loadNextPage();
   }
@@ -45,7 +45,7 @@ QUnit.test( 'checkLastPage', function( assert ) {
       append: '.post',
       scrollThreshold: false,
       history: false,
-    });
+    } );
 
     infScroll.on( 'last', onStringLast1 );
     infScroll.once( 'append', onStringAppend1 );
@@ -67,7 +67,7 @@ QUnit.test( 'checkLastPage', function( assert ) {
     infScroll.once( 'last', function() {
       assert.ok( true, 'checkLastPage: \'string\', last triggered on 3rd page' );
       setTimeout( checkPathFunction );
-    });
+    } );
 
     infScroll.loadNextPage();
   }
@@ -80,7 +80,7 @@ QUnit.test( 'checkLastPage', function( assert ) {
       // provide only page/2.html, then falsy
       path: function() {
         if ( this.pageIndex < 3 ) {
-          var nextIndex = this.pageIndex + 1;
+          let nextIndex = this.pageIndex + 1;
           return 'page/' + nextIndex + '.html';
         }
       },
@@ -88,7 +88,7 @@ QUnit.test( 'checkLastPage', function( assert ) {
       append: '.post',
       scrollThreshold: false,
       history: false,
-    });
+    } );
 
     infScroll.on( 'last', onFunctionLast2 );
     infScroll.once( 'append', onFunctionAppend2 );
@@ -108,9 +108,9 @@ QUnit.test( 'checkLastPage', function( assert ) {
       assert.ok( response, 'path: function, response there on last' );
       assert.ok( path, 'path: function, path there on last' );
       done();
-    });
+    } );
 
     infScroll.loadNextPage();
   }
 
-});
+} );
diff --git a/test/unit/history-window.js b/test/unit/history-window.js
index 0e94bd48..c59c17fd 100644
--- a/test/unit/history-window.js
+++ b/test/unit/history-window.js
@@ -1,36 +1,35 @@
 QUnit.test( 'history window', function( assert ) {
 
-  var done = assert.async();
-  var origHref = location.href;
-  var origTitle = document.title;
+  let done = assert.async();
+  let origHref = location.href;
+  let origTitle = document.title;
 
-  var demoElem = document.querySelector('.demo--history-window');
-  var infScroll = new InfiniteScroll( demoElem, {
+  let demoElem = document.querySelector('.demo--history-window');
+  let infScroll = new InfiniteScroll( demoElem, {
     path: 'page/{{#}}.html',
     append: '.post',
     scrollThreshold: false,
     history: 'replace',
     historyTitle: true,
     // debug: true,
-  });
+  } );
 
-  var page1Top = getTop( demoElem ) - 100;
-  var page2Top;
-  var page3Top;
+  let page1Top = getTop( demoElem ) - 100;
+  let page2Top, page3Top;
 
   function getTop( elem ) {
     return elem.getBoundingClientRect().top + window.pageYOffset;
   }
 
-  infScroll.once( 'append', function( response, path, items ) {
+  infScroll.once( 'append', function( response, _path, items ) {
     page2Top = getTop( items[0] );
     infScroll.once( 'history', function( title, path ) {
       assert.equal( path, location.href, '2nd page history url changed to ' + path );
       assert.equal( title, document.title, 'document title changed to ' + title );
       setTimeout( step2, 300 );
-    });
-    scrollTo( 0, page2Top - window.innerHeight/4 );
-  });
+    } );
+    scrollTo( 0, page2Top - window.innerHeight / 4 );
+  } );
 
   infScroll.loadNextPage();
 
@@ -39,7 +38,7 @@ QUnit.test( 'history window', function( assert ) {
       assert.equal( path, location.href, '1st page history, url changed to ' + path );
       assert.equal( title, document.title, 'document title changed to ' + title );
       step3();
-    });
+    } );
     scrollTo( 0, page1Top );
   }
 
@@ -50,9 +49,9 @@ QUnit.test( 'history window', function( assert ) {
         assert.equal( path, location.href, '3rd page history url changed to ' + path );
         assert.equal( title, document.title, 'document title changed to ' + title );
         allDone();
-      });
-      scrollTo( 0, page3Top - window.innerHeight/4 );
-    });
+      } );
+      scrollTo( 0, page3Top - window.innerHeight / 4 );
+    } );
     infScroll.loadNextPage();
   }
 
@@ -63,4 +62,4 @@ QUnit.test( 'history window', function( assert ) {
     done();
   }
 
-});
+} );
diff --git a/test/unit/outlayer.js b/test/unit/outlayer.js
index bf804f16..3dbcee4b 100644
--- a/test/unit/outlayer.js
+++ b/test/unit/outlayer.js
@@ -2,17 +2,17 @@
 
 QUnit.test( 'outlayer', function( assert ) {
 
-  var msnry, infScroll;
-  var demoElem = document.querySelector('.demo--outlayer');
+  let msnry, infScroll;
+  let demoElem = document.querySelector('.demo--outlayer');
 
-  var done = assert.async( 7 );
+  let done = assert.async( 7 );
 
   imagesLoaded( demoElem, function() {
 
     msnry = new Masonry( demoElem, {
       itemSelector: '.outlayer-item',
       transitionDuration: '0.1s',
-    });
+    } );
 
     infScroll = new InfiniteScroll( demoElem, {
       path: 'page/outlayer{{#}}.html',
@@ -20,7 +20,7 @@ QUnit.test( 'outlayer', function( assert ) {
       outlayer: msnry,
       history: false,
       scrollThreshold: false,
-    });
+    } );
 
     msnry.once( 'layoutComplete', onLayoutComplete2 );
     infScroll.once( 'load', done ); // confirm load event triggers
@@ -28,7 +28,7 @@ QUnit.test( 'outlayer', function( assert ) {
 
     infScroll.loadNextPage();
 
-  });
+  } );
 
   function onLayoutComplete2( items ) {
     assert.equal( items.length, 8, '8 items laid out on page 2' );
@@ -38,12 +38,12 @@ QUnit.test( 'outlayer', function( assert ) {
   }
 
   function checkItems( items ) {
-    for ( var i=0; i < items.length; i++ ) {
-      var item = items[i];
-      var itemElem = item.element;
-      assert.equal( item.element.parentNode, infScroll.element, 
-        'item ' + i + ' has infScroll parent' );
-      var leftAndTop = itemElem.style.left && itemElem.style.top;
+    for ( let i = 0; i < items.length; i++ ) {
+      let item = items[i];
+      let itemElem = item.element;
+      assert.equal( item.element.parentNode, infScroll.element,
+          'item ' + i + ' has infScroll parent' );
+      let leftAndTop = itemElem.style.left && itemElem.style.top;
       assert.ok( leftAndTop, 'item ' + i + ' has left & top style set' );
     }
   }
@@ -71,14 +71,14 @@ QUnit.test( 'outlayer', function( assert ) {
       outlayer: msnry,
       history: false,
       scrollThreshold: false,
-    });
+    } );
 
     infScroll.once( 'load', done );
     infScroll.once( 'append', function( response, path, items ) {
       assert.equal( items.length, 0, 'appended 0 items' );
       done();
-    });
+    } );
     infScroll.loadNextPage();
   }
 
-});
+} );
diff --git a/test/unit/page-index.js b/test/unit/page-index.js
index f75d34cd..e488061a 100644
--- a/test/unit/page-index.js
+++ b/test/unit/page-index.js
@@ -1,26 +1,26 @@
 QUnit.test( 'pageIndex', function( assert ) {
 
-  var demoElem = document.querySelector('.demo--page-index');
+  let demoElem = document.querySelector('.demo--page-index');
 
-  var infScroll = new InfiniteScroll( demoElem, {
+  let infScroll = new InfiniteScroll( demoElem, {
     path: '.page-index-next-link',
     history: false,
     scrollThreshold: false,
-  });
+  } );
 
   assert.equal( infScroll.pageIndex, 4, 'pageIndex from path element' );
 
   infScroll.destroy();
 
   // pageIndex from URL with {{#}} path
-  var prevURL = location.href;
+  let prevURL = location.href;
   // set URL with page number
   history.replaceState( null, document.title, 'page/7' );
   infScroll = new InfiniteScroll( demoElem, {
     path: 'page/{{#}}',
     history: false,
     scrollThreshold: false,
-  });
+  } );
 
   assert.equal( infScroll.pageIndex, 7, 'pageIndex from URL with {{#}}' );
 
@@ -28,12 +28,12 @@ QUnit.test( 'pageIndex', function( assert ) {
 
   infScroll.destroy();
 
-  history.replaceState(null, document.title, 'page?currPage=8');
+  history.replaceState( null, document.title, 'page?currPage=8' );
   infScroll = new InfiniteScroll( demoElem, {
     path: 'page?currPage={{#}}',
     history: false,
     scrollThreshold: false,
-  });
+  } );
 
   assert.equal( infScroll.pageIndex, 8, 'pageIndex from GET param with {{#}}' );
 
@@ -41,14 +41,15 @@ QUnit.test( 'pageIndex', function( assert ) {
 
   infScroll.destroy();
 
-  history.replaceState(null, document.title, 'page?currPage=8');
+  history.replaceState( null, document.title, 'page?currPage=8' );
   infScroll = new InfiniteScroll( demoElem, {
     path: 'page\\?currPage={{#}}',
     history: false,
     scrollThreshold: false,
-  });
+  } );
 
-  assert.equal( infScroll.pageIndex, 8, 'pageIndex from GET param with {{#}} and pre-escaped regexp' );
+  assert.equal( infScroll.pageIndex, 8,
+      'pageIndex from GET param with {{#}} and pre-escaped regexp' );
 
   history.replaceState( null, document.title, prevURL );
-});
+} );
diff --git a/test/unit/page-load-error.js b/test/unit/page-load-error.js
index b129355b..2b2efca5 100644
--- a/test/unit/page-load-error.js
+++ b/test/unit/page-load-error.js
@@ -1,32 +1,32 @@
 QUnit.test( 'pageLoad error', function( assert ) {
 
-  var demoElem = document.querySelector('.demo--page-load-error');
-  var done = assert.async( 2 );
+  let demoElem = document.querySelector('.demo--page-load-error');
+  let done = assert.async( 2 );
 
-  var infScroll = new InfiniteScroll( demoElem, {
+  let infScroll = new InfiniteScroll( demoElem, {
     // page not there
     path: function() {
       return 'page/4.html';
     },
     scrollThreshold: false,
     history: false,
-  });
+  } );
 
   infScroll.on( 'request', function() {
     assert.ok( true, 'request event' );
     done();
-  });
+  } );
 
   infScroll.on( 'error', function( error ) {
     assert.ok( error, 'error event, with error argument' );
     done();
-  });
+  } );
 
   infScroll.on( 'load', function() {
     assert.ok( false, 'load event should not trigger' );
     done();
-  });
+  } );
 
   infScroll.loadNextPage();
 
-});
+} );
diff --git a/test/unit/page-load.js b/test/unit/page-load.js
index 7ee3fe37..7bc4fdb9 100644
--- a/test/unit/page-load.js
+++ b/test/unit/page-load.js
@@ -1,44 +1,44 @@
 QUnit.test( 'pageLoad', function( assert ) {
 
-  var demoElem = document.querySelector('.demo--page-load');
+  let demoElem = document.querySelector('.demo--page-load');
 
-  var infScroll = new InfiniteScroll( demoElem, {
+  let infScroll = new InfiniteScroll( demoElem, {
     path: '.page-load-next-link',
     append: '.post',
     scrollThreshold: false,
     history: false,
-  });
+  } );
 
-  var done = assert.async( 7 );
+  let done = assert.async( 7 );
 
   // page 2
   infScroll.once( 'request', function( path ) {
     assert.ok( path.match('page/2.html'),
-      'request event, path has page/2.html' );
+        'request event, path has page/2.html' );
     done();
-  });
+  } );
 
   infScroll.once( 'load', function( response, path ) {
     assert.equal( response.nodeName, '#document',
-      'load event, response is document' );
+        'load event, response is document' );
     assert.ok( path.match('page/2.html'), 'load event, path has page/2.html' );
     assert.equal( infScroll.loadCount, 1, 'loadCount = 1' );
     assert.equal( infScroll.pageIndex, 2, 'pageIndex = 2' );
     done();
-  });
+  } );
 
   infScroll.once( 'append', function( response, path, items ) {
     assert.equal( response.nodeName, '#document',
-      'append event, response is document' );
+        'append event, response is document' );
     assert.ok( path.match('page/2.html'),
-      'append event, path has page/2.html' );
+        'append event, path has page/2.html' );
     assert.equal( items.length, 2, 'items argument, length 2' );
     assert.ok( demoElem.children[1] === items[0], 'item0 appended' );
     assert.ok( demoElem.children[2] === items[1], 'item1 appended' );
     assert.ok( window.page2InlineScriptLoaded, 'inline script executed' );
     done();
     setTimeout( page3 ); // do next thing
-  });
+  } );
 
   infScroll.loadNextPage();
 
@@ -48,41 +48,41 @@ QUnit.test( 'pageLoad', function( assert ) {
 
     infScroll.once( 'request', function( path ) {
       assert.ok( path.match('page/3.html'),
-        'request event, path has page/3.html' );
+          'request event, path has page/3.html' );
       done();
-    });
+    } );
 
     infScroll.once( 'load', function( response, path ) {
       assert.equal( response.nodeName, '#document',
-        'load event, response is document' );
+          'load event, response is document' );
       assert.ok( path.match('page/3.html'), 'load event, path has page/3.html' );
       assert.equal( infScroll.loadCount, 2, 'loadCount = 2' );
       assert.equal( infScroll.pageIndex, 3, 'pageIndex = 3' );
       done();
-    });
+    } );
 
     infScroll.once( 'append', function( response, path, items ) {
       assert.equal( response.nodeName, '#document',
-        'append event, response is document' );
+          'append event, response is document' );
       assert.ok( path.match('page/3.html'),
-        'append event, path has page/3.html' );
+          'append event, path has page/3.html' );
       assert.equal( items.length, 3, 'items argument, length 3' );
       assert.equal( demoElem.children[3], items[0], 'item0 appended' );
       assert.equal( demoElem.children[4], items[1], 'item1 appended' );
       assert.equal( demoElem.children[5], items[2], 'item1 appended' );
       done();
-    });
+    } );
 
     infScroll.once( 'last', function( response, path ) {
       assert.equal( response.nodeName, '#document',
-        'last event, response is document' );
+          'last event, response is document' );
       assert.ok( path.match('page/3.html'),
-        'last event, path has page/3.html' );
+          'last event, path has page/3.html' );
       done();
       // setTimeout( pageError );
-    });
+    } );
 
     infScroll.loadNextPage();
   }
 
-});
+} );
diff --git a/test/unit/path.js b/test/unit/path.js
index 0bb497c9..f6cc2b0b 100644
--- a/test/unit/path.js
+++ b/test/unit/path.js
@@ -1,16 +1,16 @@
 QUnit.test( 'path', function( assert ) {
 
   // path: function
-  var infScroll = new InfiniteScroll( '.demo--path', {
+  let infScroll = new InfiniteScroll( '.demo--path', {
     path: function() {
-      var nextIndex = this.loadCount + 1;
+      let nextIndex = this.loadCount + 1;
       return '/fn/page' + nextIndex + '.html';
     },
     scrollThreshold: false,
     history: false,
-  });
+  } );
   assert.equal( infScroll.getPath(), '/fn/page1.html',
-    'path option set with function' );
+      'path option set with function' );
   infScroll.destroy();
 
   // path: string{{#}}
@@ -18,9 +18,9 @@ QUnit.test( 'path', function( assert ) {
     path: '/string/page{{#}}.html',
     scrollThreshold: false,
     history: false,
-  });
+  } );
   assert.equal( infScroll.getPath(), '/string/page2.html',
-    'path option set with {{#}} string' );
+      'path option set with {{#}} string' );
   infScroll.destroy();
 
   // path: selector string
@@ -28,9 +28,9 @@ QUnit.test( 'path', function( assert ) {
     path: '.path-next-link',
     scrollThreshold: false,
     history: false,
-  });
+  } );
   assert.equal( infScroll.getPath(), '/area51/selector/page10.html',
-    'path option set with selector string' );
+      'path option set with selector string' );
   infScroll.destroy();
 
   // path: bad
@@ -38,8 +38,8 @@ QUnit.test( 'path', function( assert ) {
     path: '.bad-path',
     scrollThreshold: false,
     history: false,
-  });
+  } );
   assert.ok( true, 'bad path does not throw error' );
   infScroll.destroy();
 
-});
+} );
diff --git a/test/unit/prefill-element-last.js b/test/unit/prefill-element-last.js
index e3aafbd7..0abed24e 100644
--- a/test/unit/prefill-element-last.js
+++ b/test/unit/prefill-element-last.js
@@ -1,11 +1,11 @@
 QUnit.test( 'prefill element last', function( assert ) {
 
   // expected load count, each post is 200px tall
-  var expLoadCount = 2;
+  let expLoadCount = 2;
 
-  var done = assert.async( expLoadCount );
+  let done = assert.async( expLoadCount );
 
-  var infScroll = new InfiniteScroll( '.demo--prefill-element-last', {
+  let infScroll = new InfiniteScroll( '.demo--prefill-element-last', {
     path: function() {
       return this.loadCount < 2 ? 'page/prefill.html' : false;
     },
@@ -19,13 +19,13 @@ QUnit.test( 'prefill element last', function( assert ) {
       this.on( 'append', onAppend );
       this.on( 'error', onError );
     },
-  });
+  } );
 
   function onAppend() {
     assert.ok( true, 'prefill element appended post ' + infScroll.loadCount );
     if ( infScroll.loadCount == expLoadCount ) {
       assert.equal( infScroll.loadCount, expLoadCount,
-        expLoadCount + ' pages appended' );
+          expLoadCount + ' pages appended' );
     }
     done();
   }
@@ -34,4 +34,4 @@ QUnit.test( 'prefill element last', function( assert ) {
     assert.ok( false, 'error should not trigger' );
   }
 
-});
+} );
diff --git a/test/unit/prefill-element.js b/test/unit/prefill-element.js
index ab502dae..f79faad7 100644
--- a/test/unit/prefill-element.js
+++ b/test/unit/prefill-element.js
@@ -1,11 +1,11 @@
 QUnit.test( 'prefill element', function( assert ) {
 
   // expected load count, each post is 200px tall
-  var expLoadCount = 3;
+  let expLoadCount = 3;
 
-  var done = assert.async( expLoadCount );
+  let done = assert.async( expLoadCount );
 
-  var infScroll = new InfiniteScroll( '.demo--prefill-element', {
+  let infScroll = new InfiniteScroll( '.demo--prefill-element', {
     path: function() {
       return 'page/prefill.html';
     },
@@ -17,15 +17,15 @@ QUnit.test( 'prefill element', function( assert ) {
     onInit: function() {
       this.on( 'append', onAppend );
     },
-  });
+  } );
 
   function onAppend() {
     assert.ok( true, 'prefill element appended post ' + infScroll.loadCount );
     if ( infScroll.loadCount == expLoadCount ) {
       assert.equal( infScroll.loadCount, expLoadCount,
-        expLoadCount + ' pages appended' );
+          expLoadCount + ' pages appended' );
     }
     done();
   }
 
-});
+} );
diff --git a/test/unit/prefill-window.js b/test/unit/prefill-window.js
index 63873cca..357ca77d 100644
--- a/test/unit/prefill-window.js
+++ b/test/unit/prefill-window.js
@@ -1,10 +1,10 @@
 QUnit.test( 'prefill window', function( assert ) {
 
   // expected load count, each post is 200px tall
-  var expLoadCount = Math.ceil( window.innerHeight / 200 );
-  var done = assert.async( expLoadCount );
+  let expLoadCount = Math.ceil( window.innerHeight / 200 );
+  let done = assert.async( expLoadCount );
 
-  var infScroll = new InfiniteScroll( '.demo--prefill-window', {
+  let infScroll = new InfiniteScroll( '.demo--prefill-window', {
     path: function() {
       return 'page/prefill.html';
     },
@@ -15,15 +15,15 @@ QUnit.test( 'prefill window', function( assert ) {
     onInit: function() {
       this.on( 'append', onAppend );
     },
-  });
+  } );
 
   function onAppend() {
     assert.ok( true, 'prefill window appended post ' + infScroll.loadCount );
     if ( infScroll.loadCount == expLoadCount ) {
       assert.equal( infScroll.loadCount, expLoadCount,
-        expLoadCount + ' pages appended' );
+          expLoadCount + ' pages appended' );
     }
     done();
   }
 
-});
+} );
diff --git a/test/unit/scroll-watch-element.js b/test/unit/scroll-watch-element.js
index 2eacef8e..2cc08c8d 100644
--- a/test/unit/scroll-watch-element.js
+++ b/test/unit/scroll-watch-element.js
@@ -1,18 +1,18 @@
 QUnit.test( 'scrollWatch element', function( assert ) {
 
-  var done = assert.async();
+  let done = assert.async();
 
-  var demoElem = document.querySelector('.demo--scroll-watch-element');
+  let demoElem = document.querySelector('.demo--scroll-watch-element');
 
-  var infScroll = new InfiniteScroll( demoElem, {
+  let infScroll = new InfiniteScroll( demoElem, {
     path: 'page/{{#}}',
     scrollThreshold: 200,
     elementScroll: true,
     loadOnScroll: false,
     history: false,
-  });
+  } );
 
-  var bottom;
+  let bottom;
   function updateBottom() {
     bottom = demoElem.scrollHeight - demoElem.clientHeight;
   }
@@ -29,7 +29,7 @@ QUnit.test( 'scrollWatch element', function( assert ) {
     demoElem.scrollTop = 100;
     // setTimeout to trigger debounced scroll listeners
     setTimeout( step2, 300 );
-  });
+  } );
 
   // scroll close to threshold, but not over
   function step2() {
@@ -44,7 +44,7 @@ QUnit.test( 'scrollWatch element', function( assert ) {
     infScroll.once( 'scrollThreshold', function() {
       assert.ok( true, 'scrollThreshold triggered at bottom' );
       setTimeout( step4, 300 );
-    });
+    } );
     // scroll past threshold
     demoElem.scrollTop = bottom - 150;
   }
@@ -64,7 +64,7 @@ QUnit.test( 'scrollWatch element', function( assert ) {
       assert.ok( true, 'scrollThreshold triggered at new bottom' );
       infScroll.destroy();
       done();
-    });
+    } );
     demoElem.appendChild( getPost() );
     demoElem.appendChild( getPost() );
     updateBottom();
@@ -72,9 +72,9 @@ QUnit.test( 'scrollWatch element', function( assert ) {
   }
 
   function getPost() {
-    var post = document.createElement('div');
+    let post = document.createElement('div');
     post.className = 'post';
     return post;
   }
 
-});
+} );
diff --git a/test/unit/scroll-watch-window.js b/test/unit/scroll-watch-window.js
index 13b56296..4b3a48c7 100644
--- a/test/unit/scroll-watch-window.js
+++ b/test/unit/scroll-watch-window.js
@@ -1,19 +1,19 @@
 QUnit.test( 'scrollWatch window', function( assert ) {
 
-  var done = assert.async();
+  let done = assert.async();
 
-  var demoElem = document.querySelector('.demo--scroll-watch-window');
+  let demoElem = document.querySelector('.demo--scroll-watch-window');
 
-  var infScroll = new InfiniteScroll( demoElem, {
+  let infScroll = new InfiniteScroll( demoElem, {
     path: 'page/{{#}}',
     scrollThreshold: 400,
     loadOnScroll: false,
     history: false,
-  });
+  } );
 
-  var bottom;
+  let bottom;
   function updateBottom() {
-    var rect = demoElem.getBoundingClientRect();
+    let rect = demoElem.getBoundingClientRect();
     bottom = rect.bottom + window.pageYOffset - window.innerHeight;
   }
   updateBottom();
@@ -29,7 +29,7 @@ QUnit.test( 'scrollWatch window', function( assert ) {
     scrollTo( 0, 100 );
     // setTimeout to trigger debounced scroll listeners
     setTimeout( step2, 300 );
-  });
+  } );
 
   // scroll close to threshold, but not over
   function step2() {
@@ -44,7 +44,7 @@ QUnit.test( 'scrollWatch window', function( assert ) {
     infScroll.once( 'scrollThreshold', function() {
       assert.ok( true, 'scrollThreshold triggered at bottom' );
       setTimeout( step4, 300 );
-    });
+    } );
     // scroll past threshold
     scrollTo( 0, bottom - 300 );
   }
@@ -65,11 +65,11 @@ QUnit.test( 'scrollWatch window', function( assert ) {
       infScroll.destroy();
       demoElem.style.height = '';
       done();
-    });
+    } );
     demoElem.style.height = '1000px';
     updateBottom();
     scrollTo( 0, bottom - 300 );
   }
 
-});
+} );