@babel/plugin-transform-arrow-functions

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 =>
  12.       console.log(this._name + " knows " + f));
  13.   }
  14. };
  15. 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": [
  3.     ["@babel/plugin-transform-arrow-functions", { "spec": true }]
  4.   ]
  5. }

Via CLI

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

Via Node API

  1. require("@babel/core").transform("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(function (num) {
  12.   babelHelpers.newArrowCheck(this, _this);
  13.   return num * 2;
  14. }.bind(this));
  15. console.log(double); // [2,4,6]
  17. var bob = {
  18.   _name: "Bob",
  19.   _friends: ["Sally", "Tom"],
  20.   printFriends() {
  21.     var _this2 = this;
  23.     this._friends.forEach(function (f) {
  24.       babelHelpers.newArrowCheck(this, _this2);
  25.       return console.log(this._name + " knows " + f);
  26.     }.bind(this));
  27.   }
  28. };
  29. console.log(bob.printFriends());

This option enables the following:

  • Wrap the generated function in .bind(this) and keeps uses of this insidethe 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