Include es5-shim especially if your browser doesn't support ECMAScript 5 - but every JS engine requires the es5-shim to correct broken implementations, so it's strongly recommended to always include it. Additionally, es5-shim should be loaded before es6-shim.
For node.js, io.js, or any npm-managed workflow (this is the recommended method):
npm install es6-shim
Alternative methods:
component install paulmillr/es6-shim if you’re using component(1).
These methods are part of "Annex B", which means that although they are a defacto standard, you shouldn't use them. None the less, the es6-shim provides them and normalizes their behavior across browsers.
Subclassing
The Map, Set, and Promise implementations are subclassable.
You should use the following pattern to create a subclass in ES5 which will continue to work in ES6:
require('es6-shim');
function MyPromise(exec) {
var promise = new Promise(exec);
Object.setPrototypeOf(promise, MyPromise.prototype);
// ...
return promise;
}
Object.setPrototypeOf(MyPromise, Promise);
MyPromise.prototype = Object.create(Promise.prototype, {
constructor: { value: MyPromise }
});
String.prototype.normalize
Including a proper shim for String.prototype.normalize would increase the size of this library by a factor of more than 4.
So instead we recommend that you install the unorm package alongside es6-shim if you need String.prototype.normalize.
See https://github.com/paulmillr/es6-shim/issues/134 for more discussion.
WeakMap shim
It is not possible to implement WeakMap in pure javascript.
The es6-collections implementation doesn't hold values strongly, which is critical for the collection. es6-shim decided to not include an incorrect shim.
WeakMap has very unusual use-cases, so you probably won't need it at all (use simple Map instead).
Getting started
require('es6-shim');
var assert = require('assert');
assert.equal(true, 'abc'.startsWith('a'));
assert.equal(false, 'abc'.endsWith('a'));
assert.equal(true, 'john alice'.includes('john'));
assert.equal('123'.repeat(2), '123123');
assert.equal(false, NaN === NaN);
assert.equal(true, Object.is(NaN, NaN));
assert.equal(true, -0 === 0);
assert.equal(false, Object.is(-0, 0));
var result = Object.assign({ a: 1 }, { b: 2 });
assert.deepEqual(result, { a: 1, b: 2 });
assert.equal(true, isNaN('a'));
assert.equal(false, Number.isNaN('a'));
assert.equal(true, Number.isNaN(NaN));
assert.equal(true, isFinite('123'));
assert.equal(false, Number.isFinite('123'));
assert.equal(false, Number.isFinite(Infinity));
// Tests if value is a number, finite,
// >= -9007199254740992 && <= 9007199254740992 and floor(value) === value
assert.equal(false, Number.isInteger(2.4));
assert.equal(1, Math.sign(400));
assert.equal(0, Math.sign(0));
assert.equal(-1, Math.sign(-400));
var found = [5, 10, 15, 10].find(function (item) { return item / 2 === 5; });
assert.equal(10, found);
var foundIndex = [5, 10, 15, 10].findIndex(function (item) { return item / 2 === 5; });
assert.equal(1, foundIndex);
// Replacement for `{}` key-value storage.
// Keys can be anything.
var map = new Map([['Bob', 42], ['Foo', 'bar']]);
map.set('John', 25);
map.set('Alice', 400);
map.set(['meh'], 555);
assert.equal(undefined, map.get(['meh'])); // undefined because you need to use exactly the same object.
map.delete('Alice');
map.keys();
map.values();
assert.equal(4, map.size);
// Useful for storing unique items.
var set = new Set([0, 1]);
set.add(2);
set.add(5);
assert.equal(true, set.has(0));
assert.equal(true, set.has(1));
assert.equal(true, set.has(2));
assert.equal(false, set.has(4));
assert.equal(true, set.has(5));
set.delete(5);
assert.equal(false, set.has(5));
// Promises, see
// http://www.slideshare.net/domenicdenicola/callbacks-promises-and-coroutines-oh-my-the-evolution-of-asynchronicity-in-javascript
// https://github.com/petkaantonov/bluebird/#what-are-promises-and-why-should-i-use-them
Promise.resolve(5).then(function (value) {
assert.equal(value, 5);
if (value) throw new Error('whoops!');
// do some stuff
return anotherPromise();
}).catch(function (e) {
assert.equal(e.message, 'whoops!');
assert.equal(true, e instanceof Error);
// any errors thrown asynchronously end up here
});
Caveats
Object.setPrototypeOf / Reflect.setPrototypeOf
Note that null objects (Object.create(null), eg, an object with null as its [[Prototype]]) can not have their [[Prototype]] changed except via a native Object.setPrototypeOf.
Well-known Symbols
In order to make them work cross-realm, these are created with the global Symbol registry via Symbol.for. This does not violate the spec, but it does mean that Symbol.for('Symbol.search') === Symbol.search will be true, which it would not by default in a fresh compliant realm.
