babel/README.md

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**6to5** turns ES6 code into vanilla ES5, so you can use ES6 features **today.**

 - **Fast** - no redundant code added so your compiled code is as fast as possible.
 - **Extensible** - with a large range of [plugins](#plugins).
 - **Lossless** - **source map support** so you can debug your compiled code with ease.
 - **Compact** - maps directly to the equivalent ES5 with **no runtime**.
 - **Concise** - does not pollute scope with unneccesary variables.

## Installation

    $ npm install -g 6to5

## Plugins

 - [Browserify](https://github.com/sebmck/6to5-browserify)
 - [Connect Middleware](https://github.com/sebmck/6to5-connect)

### Community

 - Broccoli
 - [Brunch](https://github.com/es128/6to5-brunch)
 - [Gulp](https://github.com/sindresorhus/gulp-6to5)
 - [Grunt](https://github.com/sindresorhus/grunt-6to5)

## [Features](FEATURES.md)

 - [Array comprehension](FEATURES.md#array-comprehension)
 - [Arrow functions](FEATURES.md#arrow-functions)
 - [Block binding](FEATURES.md#block-binding)
 - [Classes](FEATURES.md#classes)
 - [Computed property names](FEATURES.md#computed-property-names)
 - [Constants](FEATURES.md#constants)
 - [Default parameters](FEATURES.md#default-parameters)
 - [Destructuring](FEATURES.md#destructuring)
 - [For-of](FEATURES.md#for-of)
 - [Modules](FEATURES.md#modules)
 - [Numeric literals](FEATURES.md#numeric-literals)
 - [Property method assignment](FEATURES.md#property-method-assignment)
 - [Property name shorthand](FEATURES.md#property-name-shorthand)
 - [Rest parameters](FEATURES.md#rest-parameters)
 - [Spread](FEATURES.md#spread)
 - [Template literals](FEATURES.md#template-literals)

To be implemented:

 - [Generators](FEATURES.md#generators)

## Usage

### CLI

Compile the file `script.js` and output it to `script-compiled.js`.

    $ 6to5 script.js -o script-compiled.js

Compile the entire `src` directory and output it to the `lib` directory.

    $ 6to5 src -d lib

Compile the file `script.js` and output it to stdout.

    $ 6to5 script.js

#### Node

Launch a repl.

    $ 6to5-node

Evaluate code.

    $ 6to5-node -e "class Test { }"

Compile and run `test.js`.

    $ 6to5-node test

### Node

```javascript
var to5 = require("6to5");

to5.transform("code();");

to5.transformFileSync("filename.js");

to5.transformFile("filename.js", function (err, data) {

});
```

##### Options

```javascript
to5.transform("code();", {
  // List of transformers to EXCLUDE
  // This is a camelised version of the name found in `features`
  // eg. "Arrow functions" is "arrowFunctions"
  blacklist: [],

  // List of transformers to ONLY use.
  // See `blacklist` for naming scheme.
  whitelist: [],

  // Append source map and comment to bottom of returned output.
  sourceMap: false,

  // Returns an object `{ code: "", map: {} }` instead of an appended string.
  sourceMapObject: false,

  // Filename for use in errors etc.
  filename: "unknown",

  // Format options
  // See https://github.com/Constellation/escodegen/wiki/API for options.
  format: {}
});
```

#### Require hook

All subsequent files required by node will be transformed into ES5 compatible
code. An ES6 polyfill is also required negating the
[polyfill caveat](#polyfill).

```javascript
require("6to5/register");
```

## Caveats

### Polyfill

6to5 does not include a runtime nor polyfill and it's up to the developer to
include one in compiled browser code.

A polyfill is included with 6to5 code that can be included in node like so:

```javascript
require("6to5/polyfill");
```

This is simply a wrapper around the
[es6-shim](https://github.com/paulmillr/es6-shim) and
[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.

When using the [require hook](#require-hook) the aforementioned polyfill is
required.

If you're planning on using 6to5 output in the browser then it's up to you
to include polyfills. [es6-symbol](https://github.com/medikoo/es6-symbol#browser)
and [es6-shim](https://raw.githubusercontent.com/paulmillr/es6-shim/master/es6-shim.js)
support the vast majority of polyfill concerns.

#### For-of

Iterator/Symbol polyfill required.

### Classes

Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
limitations in ES5 implementations.

## Comparison to Traceur

6to5 is different to Traceur in a few very distinct ways.

### Runtime

Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
While this can be trimmed down by selectively building the runtime, it's an
unneccesary step when a runtime can be eliminated entirely.

Instead of mapping to a runtime, 6to5 maps directly to the equivalent ES5. This
means that your transpiled code will be as simple as possible.

### Performance