/Babel 6

ES2015 classes transform

Compile ES2015 classes to ES5


Built-in classes such as Date, Array, DOM etc cannot be properly subclassed due to limitations in ES5 (for the es2015-classes plugin). You can try to use babel-plugin-transform-builtin-extend based on Object.setPrototypeOf and Reflect.construct, but it also has some limitations.


npm install --save-dev babel-plugin-transform-es2015-classes



// without options
  "plugins": ["transform-es2015-classes"]

// with options
  "plugins": [
    ["transform-es2015-classes", {
      "loose": true


babel --plugins transform-es2015-classes script.js

Via Node API

require("babel-core").transform("code", {
  plugins: ["transform-es2015-classes"]



boolean, defaults to false.

Method enumerability

Please note that in loose mode class methods are enumerable. This is not in line with the spec and you may run into issues.

Method assignment

Under loose mode, methods are defined on the class prototype with simple assignments instead of being defined. This can result in the following not working:

class Foo {
  set bar() {
    throw new Error("foo!");

class Bar extends Foo {
  bar() {
    // will throw an error when this method is defined

When Bar.prototype.foo is defined it triggers the setter on Foo. This is a case that is very unlikely to appear in production code however it’s something to keep in mind.

© 2018 Sebastian McKenzie
Licensed under the MIT License.