# @babel/plugin-transform-arrow-functions

> Compile ES2015 arrow functions to ES5

## Example

**In**

```javascript
var a = () => {};
var a = (b) => b;

const double = [1,2,3].map((num) => num * 2);
console.log(double); // [2,4,6]

var bob = {
  _name: "Bob",
  _friends: ["Sally", "Tom"],
  printFriends() {
    this._friends.forEach(f =>
      console.log(this._name + " knows " + f));
  }
};
console.log(bob.printFriends());
```

**Out**

```javascript
var a = function () {};
var a = function (b) {
  return b;
};

const double = [1, 2, 3].map(function (num) {
  return num * 2;
});
console.log(double); // [2,4,6]

var bob = {
  _name: "Bob",
  _friends: ["Sally", "Tom"],
  printFriends() {
    var _this = this;

    this._friends.forEach(function (f) {
      return console.log(_this._name + " knows " + f);
    });
  }
};
console.log(bob.printFriends());
```

## Installation

```sh
npm install --save-dev @babel/plugin-transform-arrow-functions
```

## Usage

### Via `.babelrc` (Recommended)

**.babelrc**

Without options:

```json
{
  "plugins": ["@babel/plugin-transform-arrow-functions"]
}
```

With options:

```json
{
  "plugins": [
    ["@babel/plugin-transform-arrow-functions", { "spec": true }]
  ]
}
```

### Via CLI

```sh
babel --plugins @babel/plugin-transform-arrow-functions script.js
```

### Via Node API

```javascript
require("@babel/core").transform("code", {
  plugins: ["@babel/plugin-transform-arrow-functions"]
});
```

## Options

### `spec`

`boolean`, defaults to `false`.

<p><details>
  <summary><b>Example</b></summary>

  Using spec mode with the above example produces:

  ```js
  var _this = this;

  var a = function a() {
    babelHelpers.newArrowCheck(this, _this);
  }.bind(this);
  var a = function a(b) {
    babelHelpers.newArrowCheck(this, _this);
    return b;
  }.bind(this);

  const double = [1, 2, 3].map(function (num) {
    babelHelpers.newArrowCheck(this, _this);
    return num * 2;
  }.bind(this));
  console.log(double); // [2,4,6]

  var bob = {
    _name: "Bob",
    _friends: ["Sally", "Tom"],
    printFriends() {
      var _this2 = this;

      this._friends.forEach(function (f) {
        babelHelpers.newArrowCheck(this, _this2);
        return console.log(this._name + " knows " + f);
      }.bind(this));
    }
  };
  console.log(bob.printFriends());
  ```
</details></p>

This option enables the following:

 - Wrap the generated function in `.bind(this)` and keeps uses of `this` inside
   the function as-is, instead of using a renamed `this`.

 - Add a runtime check to ensure the functions are not instantiated.

 - Add names to arrow functions.