Add Amazon Price conversion script

Author: carltonf

amazon-convert.user.js

@@ -0,0 +1,101 @@
+// ==UserScript==
+// @name        Amazon Currency Conversion
+// @namespace   carltonf.github.io
+// @description Automatically converts different currencies into your home currency, more convenient for overseas shopping.
+// @include     http://www.amazon.com/*
+// @include     http://www.amazon.co.jp/*
+// @version     0.3
+// @grant       none
+// ==/UserScript==
+
+'use strict';
+
+// * Extra info
+var CurSymMap = {
+  'CNY': '¥',
+  // amazon.co.jp uses a Yen symbol in JP locale (it seems)
+  'JPY': '￥',
+  'USD': '$',
+};
+
+// As 2015-10-31
+var CurRates = {
+  'JPY-CNY': 0.05237,
+  'USD-CNY': 6.3185,
+}
+
+// * Setup
+// Get the 
+var origCur = null;
+switch (document.location.hostname){
+case "www.amazon.com":
+  origCur = 'USD';
+  break;
+case "www.amazon.co.jp":
+  origCur = 'JPY';
+  break;
+default:
+  throw new Error(`${document.location.hostname} is NOT supported!`);
+}
+
+// * Main converter for price
+// for now only 'CNY' as target, so targetCur is pre-fixed.
+function PriceConverter (origCur, targetCur){
+  var self = this;
+
+
+  this._origCur = origCur;
+  this._targetCur = targetCur || 'CNY';
+
+  // ** Price string conversion
+  // accept a string in format like "$ 130" and outputs a string in the target
+  // currency.
+  this.convertPriceStr = convertPriceStr
+  function convertPriceStr(str){
+    var origSym = CurSymMap[self._origCur],
+        targetSym = CurSymMap[self._targetCur],
+        origNum = -1,
+        targetNum = -1;
+
+    // *** Extract the number part
+    str = str.substring( str.indexOf(origSym) + 1 ).trim().replace(',', '');
+    origNum = Number(str);
+
+    // *** Convert currency
+    targetNum = origNum * CurRates[`${self._origCur}-${self._targetCur}`];
+
+    // *** output in the currency
+    // TODO the locale is fixed to Chinese
+    var numberFormat = new Intl.NumberFormat("zh-Hans-CN",
+                                             { style: 'currency',
+                                               currency: this._targetCur,
+                                               maximumFractionDigits: 1,
+                                             });
+
+    // also separates the symbol and number with a space
+    // with right locale, no need to add currency symbol manually
+    return numberFormat.format(targetNum);
+  };
+}
+
+var priceConverter = new PriceConverter(origCur);
+
+// * Mainpulate the page price tags
+// Return an array of elements
+function getPriceTagAll(){
+  function isPriceTag (elm){
+    return elm.textContent.includes(CurSymMap[origCur]);
+  }
+
+  var priceTags = [].filter.call(document.querySelectorAll('span'),
+                                 isPriceTag);
+
+  return priceTags;
+}
+
+
+function changePriceTag(priceTag){
+  priceTag.innerText = priceConverter.convertPriceStr(priceTag.textContent);
+}
+
+getPriceTagAll().forEach(changePriceTag);