Gigasecond solution

Author: eprunier

gigasecond/README.md

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+# Gigasecond
+
+Calculate the moment when someone has lived for 10^9 seconds.
+
+A gigasecond is 10^9 (1,000,000,000) seconds.
+
+## Setup
+
+Go through the setup instructions for JavaScript to
+install the necessary dependencies:
+
+http://exercism.io/languages/javascript
+
+## Making the Test Suite Pass
+
+Execute the tests with:
+
+    jasmine-node .
+
+In many test suites all but the first test have been skipped.
+
+Once you get a test passing, you can unskip the next one by
+changing `xit` to `it`.
+
+## Source
+
+Chapter 9 in Chris Pine's online Learn to Program tutorial. [http://pine.fm/LearnToProgram/?Chapter=09](http://pine.fm/LearnToProgram/?Chapter=09)
+
+## Submitting Incomplete Problems
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+

gigasecond/gigasecond.js

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+const Gigasecond = function (date) {
+	this.value = date;
+};
+
+const msToAdd = Math.pow(10, 9) * 1000;
+
+Gigasecond.prototype.date = function () {
+	const time = this.value.getTime();
+	return new Date(time + msToAdd);
+};
+
+module.exports = Gigasecond;

gigasecond/gigasecond.spec.js

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+var Gigasecond = require('./gigasecond');
+
+describe('Gigasecond', function() {
+
+  it('tells a gigasecond anniversary since midnight', function() {
+    var gs = new Gigasecond(new Date(Date.UTC(2015, 8, 14)));
+    var expectedDate = new Date(Date.UTC(2047, 4, 23, 1, 46, 40));
+    expect(gs.date()).toEqual(expectedDate);
+  });
+
+  it('tells the anniversary is next day when you are born at night', function() {
+    var gs = new Gigasecond(new Date(Date.UTC(2015, 8, 14, 23, 59, 59)));
+    var expectedDate = new Date(Date.UTC(2047, 4, 24, 1, 46, 39));
+    expect(gs.date()).toEqual(expectedDate);
+  });
+
+  it('even works before 1970 (beginning of Unix epoch)', function() {
+    var gs = new Gigasecond(new Date(Date.UTC(1959, 6, 19, 5, 13, 45)));
+    var expectedDate = new Date(Date.UTC(1991, 2, 27, 7, 0, 25));
+    expect(gs.date()).toEqual(expectedDate);
+  });
+
+  it('make sure calling "date" doesn\'t mutate value', function() {
+    var gs = new Gigasecond(new Date(Date.UTC(1959, 6, 19, 5, 13, 45)));
+    var expectedDate = new Date(Date.UTC(1991, 2, 27, 7, 0, 25));
+    gs.date();
+    expect(gs.date()).toEqual(expectedDate);
+  });
+});
+
+