@babel/plugin-transform-arrow-functions

NOTE: This plugin is included in @babel/preset-env

Example

In

  1. var a = () => {};
  2. var a = b => b;
  4. const double = [1, 2, 3].map(num => num * 2);
  5. console.log(double); // [2,4,6]
  7. var bob = {
  8.   _name: "Bob",
  9.   _friends: ["Sally", "Tom"],
  10.   printFriends() {
  11.     this._friends.forEach(f => console.log(this._name + " knows " + f));
  12.   },
  13. };
  14. console.log(bob.printFriends());

Out

  1. var a = function() {};
  2. var a = function(b) {
  3.   return b;
  4. };
  6. const double = [1, 2, 3].map(function(num) {
  7.   return num * 2;
  8. });
  9. console.log(double); // [2,4,6]
  11. var bob = {
  12.   _name: "Bob",
  13.   _friends: ["Sally", "Tom"],
  14.   printFriends() {
  15.     var _this = this;
  17.     this._friends.forEach(function(f) {
  18.       return console.log(_this._name + " knows " + f);
  19.     });
  20.   },
  21. };
  22. console.log(bob.printFriends());

Installation

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

Usage

With a configuration file (Recommended)

Without options:

  1. {
  2.   "plugins": ["@babel/plugin-transform-arrow-functions"]
  3. }

With options:

  1. {
  2.   "plugins": [["@babel/plugin-transform-arrow-functions", { "spec": true }]]
  3. }

Via CLI

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

Via Node API

  1. require("@babel/core").transformSync("code", {
  2.   plugins: ["@babel/plugin-transform-arrow-functions"],
  3. });

Options

spec

boolean, defaults to false.

Example

Using spec mode with the above example produces:

  1. var _this = this;
  3. var a = function a() {
  4.   babelHelpers.newArrowCheck(this, _this);
  5. }.bind(this);
  6. var a = function a(b) {
  7.   babelHelpers.newArrowCheck(this, _this);
  8.   return b;
  9. }.bind(this);
  11. const double = [1, 2, 3].map(
  12.   function(num) {
  13.     babelHelpers.newArrowCheck(this, _this);
  14.     return num * 2;
  15.   }.bind(this)
  16. );
  17. console.log(double); // [2,4,6]
  19. var bob = {
  20.   _name: "Bob",
  21.   _friends: ["Sally", "Tom"],
  22.   printFriends() {
  23.     var _this2 = this;
  25.     this._friends.forEach(
  26.       function(f) {
  27.         babelHelpers.newArrowCheck(this, _this2);
  28.         return console.log(this._name + " knows " + f);
  29.       }.bind(this)
  30.     );
  31.   },
  32. };
  33. 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.

You can read more about configuring plugin options here