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@babel/plugin-transform-arrow-functions

info

This plugin is included in @babel/preset-env

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​

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

Usage​

Without options:

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

With options:

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

Via CLI​

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

Via Node API​

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

Options​

spec​

boolean, defaults to false.

Example

Using spec mode with the above example produces:

JavaScript
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());

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.

tip

You can read more about configuring plugin options here