es6-shim

What is es6-shim?

The es6-shim package is designed to provide compatibility shims so that legacy JavaScript engines behave as closely as possible to ECMAScript 6 (ES6). It includes shims for new methods and functions introduced in ES6, allowing developers to use these features in environments that do not yet support them natively.

What are es6-shim's main functionalities?

Array.prototype methods

Adds new methods to Array.prototype like find, findIndex, etc., enabling more expressive operations on arrays.

[1, 2, 3].find(x => x == 2)

String.prototype methods

Introduces new String methods such as startsWith, endsWith, and includes for easier string manipulation.

'hello'.startsWith('hell')

Number properties

Provides new static properties and methods on the Number object like isNaN and isFinite for improved number checking.

Number.isNaN(NaN)

Promises

Implements Promises for asynchronous programming, following the ES6 specification.

new Promise(function(resolve, reject) { resolve(42); })

Maps and Sets

Adds support for new collection types such as Map and Set, offering more options for data storage and manipulation.

new Map([[1, 'one'], [2, 'two']])

Other packages similar to es6-shim

core-js

A modular standard library for JavaScript, including polyfills for ECMAScript up to 2021. Offers broader coverage than es6-shim, including proposals not yet standardized.

babel-polyfill

Part of Babel, this package includes a custom regenerator runtime and core-js. It's more comprehensive but has been deprecated in favor of directly including core-js and the regenerator-runtime.

es5-shim

Focuses on ensuring ECMAScript 5 compatibility, providing shims for older JavaScript engines. It's more focused on ES5, making it complementary rather than directly comparable to es6-shim.

README

ES6 Shim

Provides compatibility shims so that legacy JavaScript engines behave as closely as possible to ECMAScript 6 (Harmony).

Installation

If you want to use it in browser:

• Just include es6-shim before your scripts.
• Include es5-shim if your browser doesn't support ECMAScript 5.
• component install paulmillr/es6-shim if you’re using component(1).
• bower install es6-shim if you’re using Twitter Bower.

For node.js:

npm install es6-shim

In both browser and node you may also want to include unorm; see the String.prototype.normalize section for details.

Safe shims

• Map, Set (requires ES5)
• Promise
• String:
  • fromCodePoint() (a standalone shim is also available)
  • raw()
• String.prototype:
  • codePointAt() (a standalone shim is also available)
  • repeat() (a standalone shim is also available)
  • startsWith() (a standalone shim is also available)
  • endsWith() (a standalone shim is also available)
  • includes() (a standalone shim is also available)
• Number:
  • MAX_SAFE_INTEGER
  • MIN_SAFE_INTEGER
  • EPSILON
  • parseInt()
  • parseFloat()
  • isNaN()(a standalone shim is also available)
  • isInteger()
  • isSafeInteger()
  • isFinite()
• Array:
  • from() (a standalone shim is also available)
  • of() (a standalone shim is also available)
• Array.prototype:
  • copyWithin()
  • fill()
  • find() (a standalone shim is also available)
  • findIndex() (a standalone shim is also available)
  • keys() (note: keys/values/entries return an ArrayIterator object)
  • entries()
  • values()
• Object:
  • getPropertyDescriptor() (ES5)
  • getPropertyNames() (ES5)
  • getPropertyKeys() (ES5)
  • keys() (ES5, but no longer throws on non-object non-null/undefined values in ES6)
  • is() (a standalone shim is also available)
  • assign() (a standalone shim is also available)
  • setPrototypeOf() (IE >= 11)
• Math:
  • acosh()
  • asinh()
  • atanh()
  • cbrt()
  • clz32()
  • cosh()
  • expm1()
  • hypot()
  • log2()
  • log10()
  • log1p()
  • sign()
  • sinh()
  • tanh()
  • trunc()
  • imul()
  • fround()

Math functions accuracy is 1e-11.

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:

function MyPromise(exec) {
  Promise.call(this, exec);
  // ...
}
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 a very unusual use-case so you probably won't need it at all (use simple Map instead).

Getting started

'abc'.startsWith('a') // true
'abc'.endsWith('a') // false
'john alice'.includes('john') // true
'123'.repeat(2)     // '123123'

Object.is(NaN, NaN) // Fixes ===. 0 isnt -0, NaN is NaN
Object.assign({a: 1}, {b: 2}) // {a: 1, b: 2}

Number.isNaN('123') // false. isNaN('123') will give true.
Number.isFinite('asd') // false. Global isFinite() will give true.
// Tests if value is a number, finite,
// >= -9007199254740992 && <= 9007199254740992 and floor(value) === value
Number.isInteger(2.4) // false.

Math.sign(400) // 1, 0 or -1 depending on sign. In this case 1.

[5, 10, 15, 10].find(function (item) {return item / 2 === 5;}) // 10
[5, 10, 15, 10].findIndex(function (item) {return item / 2 === 5;}) // 1

// Replacement for `{}` key-value storage.
// Keys can be anything.
var map = new Map()
map.set('John', 25)
map.set('Alice', 400)
map.set(['meh'], 555)
map.get(['meh']) // undefined because you need to use exactly the same object.
map.delete('Alice')
map.keys()
map.values()
map.size // 2

// Useful for storing unique items.
var set = new Set()
set.add(1)
set.add(5)
set.has(1)
set.has(4)  // => false
set.delete(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) {
  if ( ... ) throw new Error("whoops!");
  // do some stuff
  return anotherPromise();
}).catch(function (e) {
  // any errors thrown asynchronously end up here
});

Other stuff:

• ECMAScript 6 drafts
• Harmony proposals

License

The project was initially based on es6-shim by Axel Rauschmayer.

Current maintainers are: Paul Miller, Jordan Harband, and C. Scott Ananian.

The MIT License (MIT)

Copyright (c) 2013-2014 Paul Miller (http://paulmillr.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Changelog

es6-shim 0.21.0 (21 Nov 2014)

• String#contains → String#includes per 2014-11-19 TC39 meeting
• Use an invalid identifier as the es6-shim iterator key, so it doesn’t show up in the console as easily.