@babel/plugin-proposal-decorators

Example

Simple class decorator

JavaScript

@annotation
class MyClass {}

function annotation(target) {
  target.annotated = true;
}

Class decorator

JavaScript

@isTestable(true)
class MyClass {}

function isTestable(value) {
  return function decorator(target) {
    target.isTestable = value;
  };
}

Class method decorator

JavaScript

class C {
  message = "hello!";

  @bound
  m() {
    console.log(this.message);
  }
}

function bound(value, { name, addInitializer }) {
  addInitializer(function () {
    this[name] = this[name].bind(this);
  });
}

Installation

npm

npm install --save-dev @babel/plugin-proposal-decorators

Yarn

yarn add --dev @babel/plugin-proposal-decorators

pnpm

pnpm add --save-dev @babel/plugin-proposal-decorators

Usage

With a configuration file (Recommended)

babel.config.json

{
  "plugins": [
    ["@babel/plugin-proposal-decorators", { "version": "2023-05" }]
  ]
}

Via Node API

JavaScript

require("@babel/core").transformSync("code", {
  plugins: [
    ["@babel/plugin-proposal-decorators", { version: "2023-05" }],
  ]
});

Options

History

Version	Changes
v7.22.0	Added support for version: "2023-05"
v7.21.0	Added support for version: "2023-01"
v7.19.0	Added support for version: "2022-03"
v7.17.0	Added the version option with support for "2021-12", "2018-09" and "legacy"

version

"2023-05", "2023-01", "2022-03", "2021-12", "2018-09" or "legacy".

Selects the decorators proposal to use:

• "2023-05" is the proposal version after the updates that reached consensus in the March and May 2023 TC39 meetings, integrating these changes.
• "2023-01" is the proposal version after the updates that reached consensus in the January 2023 TC39 meeting, integrating pzuraq/ecma262#4.
• "2022-03" is the proposal version that reached consensus for Stage 3 in the March 2022 TC39 meeting. You can read more about it at tc39/proposal-decorators@8ca65c046d.
• "2021-12" is the proposal version as it was presented to TC39 in Dec 2021. You can read more about it at tc39/proposal-decorators@d6c056fa06.
• "2018-09" is the proposal version that was initially promoted to Stage 2 presented to TC39 in Sept 2018. You can read more about it at tc39/proposal-decorators@7fa580b40f.
• legacy is the legacy Stage 1 proposal, defined at wycats/javascript-decorators@e1bf8d41bf.

caution

Babel 8 will only support "2023-05" and "legacy". If you are using a different decorators version, it's recommended to migrate to "2023-05".

The spec repo provides a brief summary of the differences between these versions.

If you specify the decoratorsBeforeExport option, version defaults to "2018-09", otherwise it is a required option.

decoratorsBeforeExport

This option:

• is disallowed when using version: "legacy", version: "2022-03", version: "2023-01", or version: "2023-05";
• is required when using version: "2018-09";
• is optional and defaults to false when using version: "2021-12".

boolean

JavaScript

// decoratorsBeforeExport: false
export @decorator class Bar {}

// decoratorsBeforeExport: true
@decorator
export class Foo {}

This option was originally added to help tc39 collect feedback from the community by allowing experimentation with the proposed syntaxes. The proposal has now settled on allowing decorators either before or after export.

legacy

Deprecated

Use version: "legacy" instead. This option is a legacy alias.

boolean, defaults to false.

Use the legacy (stage 1) decorators syntax and behavior.

NOTE: Compatibility with @babel/plugin-transform-class-properties

If you are including your plugins manually and using @babel/plugin-transform-class-properties or @babel/plugin-private-methods and legacy decorators, make sure that @babel/plugin-proposal-decorators comes before @babel/plugin-transform-class-properties.

babel.config.json

{
  "plugins": [
-   "@babel/plugin-transform-class-properties",
    ["@babel/plugin-proposal-decorators", { "version": "legacy" }]
+   "@babel/plugin-transform-class-properties"
  ]
}

If you are already using @babel/preset-env, you can safely remove @babel/plugin-transform-class-properties and @babel/plugin-private-methods:

babel.config.json

{
  "presets": ["@babel/preset-env"],
  "plugins": [
-   "@babel/plugin-transform-class-properties",
    ["@babel/plugin-proposal-decorators", { "version": "legacy" }]
  ]
}

tip

You can read more about configuring plugin options here

References

• Proposal: JavaScript Decorators