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# @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.
|
