217 lines
7.7 KiB
Markdown
217 lines
7.7 KiB
Markdown
# ES6 Shim
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Provides compatibility shims so that legacy JavaScript engines behave as
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closely as possible to ECMAScript 6 (Harmony).
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[![Build Status][1]][2] [![dependency status][3]][4] [![dev dependency status][5]][6]
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[](https://ci.testling.com/paulmillr/es6-shim)
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[](https://saucelabs.com/u/es6-shim)
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## Installation
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If you want to use it in browser:
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* Just include es6-shim before your scripts.
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* Include [es5-shim](https://github.com/kriskowal/es5-shim) if your browser doesn't support ECMAScript 5.
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* `component install paulmillr/es6-shim` if you’re using [component(1)](https://github.com/component/component).
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* `bower install es6-shim` if you’re using [Twitter Bower](http://bower.io/).
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For node.js:
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npm install es6-shim
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In both browser and node you may also want to include `unorm`; see the
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[`String.prototype.normalize`](#stringprototypenormalize) section for
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details.
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## Safe shims
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* `Map`, `Set` (requires ES5)
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* `Promise`
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* `String`:
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* `fromCodePoint()` ([a standalone shim is also available](http://mths.be/fromcodepoint))
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* `raw()`
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* `String.prototype`:
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* `codePointAt()` ([a standalone shim is also available](http://mths.be/codepointat))
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* `repeat()` ([a standalone shim is also available](http://mths.be/repeat))
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* `startsWith()` ([a standalone shim is also available](http://mths.be/startswith))
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* `endsWith()` ([a standalone shim is also available](http://mths.be/endswith))
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* `contains()` ([a standalone shim is also available](http://mths.be/contains))
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* `Number`:
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* `MAX_SAFE_INTEGER`
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* `MIN_SAFE_INTEGER`
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* `EPSILON`
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* `parseInt()`
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* `parseFloat()`
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* `isNaN()`([a standalone shim is also available](https://npmjs.org/package/is-nan))
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* `isInteger()`
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* `isSafeInteger()`
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* `isFinite()`
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* `Array`:
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* `from()` ([a standalone shim is also available](https://npmjs.org/package/array.from))
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* `of()` ([a standalone shim is also available](https://npmjs.org/package/array.of))
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* `Array.prototype`:
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* `copyWithin()`
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* `fill()`
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* `find()` ([a standalone shim is also available](https://github.com/paulmillr/Array.prototype.find))
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* `findIndex()` ([a standalone shim is also available](https://github.com/paulmillr/Array.prototype.findIndex))
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* `keys()` (note: keys/values/entries return an `ArrayIterator` object)
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* `entries()`
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* `values()`
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* `Object`:
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* `getPropertyDescriptor()` (ES5)
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* `getPropertyNames()` (ES5)
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* `getPropertyKeys()` (ES5)
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* `keys()` (ES5, but no longer throws on non-object non-null/undefined values in ES6)
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* `is()` ([a standalone shim is also available](https://github.com/ljharb/object-is))
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* `assign()` ([a standalone shim is also available](https://github.com/ljharb/object.assign))
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* `setPrototypeOf()` (IE >= 11)
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* `Math`:
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* `acosh()`
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* `asinh()`
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* `atanh()`
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* `cbrt()`
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* `clz32()`
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* `cosh()`
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* `expm1()`
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* `hypot()`
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* `log2()`
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* `log10()`
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* `log1p()`
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* `sign()`
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* `sinh()`
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* `tanh()`
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* `trunc()`
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* `imul()`
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* `fround()`
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Math functions accuracy is 1e-11.
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## Subclassing
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The `Map`, `Set`, and `Promise` implementations are subclassable.
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You should use the following pattern to create a subclass in ES5 which
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will continue to work in ES6:
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```javascript
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function MyPromise(exec) {
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Promise.call(this, exec);
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// ...
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}
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Object.setPrototypeOf(MyPromise, Promise);
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MyPromise.prototype = Object.create(Promise.prototype, {
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constructor: { value: MyPromise }
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});
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```
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## String.prototype.normalize
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Including a proper shim for `String.prototype.normalize` would
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increase the size of this library by a factor of more than 4.
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So instead we recommend that you install the
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[`unorm`](https://github.com/walling/unorm)
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package alongside `es6-shim` if you need `String.prototype.normalize`.
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See https://github.com/paulmillr/es6-shim/issues/134 for more
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discussion.
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## WeakMap shim
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It is not possible to implement WeakMap in pure javascript.
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The [es6-collections](https://github.com/WebReflection/es6-collections)
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implementation doesn't hold values strongly, which is critical
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for the collection. es6-shim decided to not include an incorrect shim.
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WeakMap has a very unusual use-case so you probably won't need it at all
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(use simple `Map` instead).
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## Getting started
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```javascript
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'abc'.startsWith('a') // true
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'abc'.endsWith('a') // false
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'john alice'.contains('john') // true
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'123'.repeat(2) // '123123'
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Object.is(NaN, NaN) // Fixes ===. 0 isnt -0, NaN is NaN
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Object.assign({a: 1}, {b: 2}) // {a: 1, b: 2}
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Number.isNaN('123') // false. isNaN('123') will give true.
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Number.isFinite('asd') // false. Global isFinite() will give true.
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// Tests if value is a number, finite,
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// >= -9007199254740992 && <= 9007199254740992 and floor(value) === value
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Number.isInteger(2.4) // false.
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Math.sign(400) // 1, 0 or -1 depending on sign. In this case 1.
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[5, 10, 15, 10].find(function (item) {return item / 2 === 5;}) // 10
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[5, 10, 15, 10].findIndex(function (item) {return item / 2 === 5;}) // 1
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// Replacement for `{}` key-value storage.
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// Keys can be anything.
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var map = new Map()
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map.set('John', 25)
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map.set('Alice', 400)
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map.set(['meh'], 555)
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map.get(['meh']) // undefined because you need to use exactly the same object.
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map.delete('Alice')
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map.keys()
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map.values()
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map.size // 2
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// Useful for storing unique items.
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var set = new Set()
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set.add(1)
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set.add(5)
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set.has(1)
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set.has(4) // => false
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set.delete(5)
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// Promises, see
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// http://www.slideshare.net/domenicdenicola/callbacks-promises-and-coroutines-oh-my-the-evolution-of-asynchronicity-in-javascript
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// https://github.com/petkaantonov/bluebird/#what-are-promises-and-why-should-i-use-them
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Promise.resolve(5).then(function (value) {
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if ( ... ) throw new Error("whoops!");
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// do some stuff
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return anotherPromise();
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}).catch(function (e) {
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// any errors thrown asynchronously end up here
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});
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```
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Other stuff:
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* [ECMAScript 6 drafts](http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts)
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* [Harmony proposals](http://wiki.ecmascript.org/doku.php?id=harmony:harmony)
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## License
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The project was initially based on [es6-shim by Axel Rauschmayer](https://github.com/rauschma/es6-shim).
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Current maintainers are: [Paul Miller](http://paulmillr.com), [Jordan Harband](https://github.com/ljharb), and [C. Scott Ananian](http://cscott.net).
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The MIT License (MIT)
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Copyright (c) 2013-2014 Paul Miller (http://paulmillr.com)
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Permission is hereby granted, free of charge, to any person obtaining a copy of
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this software and associated documentation files (the "Software"), to deal in
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the Software without restriction, including without limitation the rights to
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use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
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of the Software, and to permit persons to whom the Software is furnished to do
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so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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[1]: https://travis-ci.org/paulmillr/es6-shim.svg
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[2]: https://travis-ci.org/paulmillr/es6-shim
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[3]: https://david-dm.org/paulmillr/es6-shim.svg
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[4]: https://david-dm.org/paulmillr/es6-shim
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[5]: https://david-dm.org/paulmillr/es6-shim/dev-status.svg
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[6]: https://david-dm.org/paulmillr/es6-shim#info=devDependencies
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