@babel/plugin-transform-private-methods
This plugin is included in @babel/preset-env
, in ES2022
History
Version | Changes |
---|---|
v7.3.0 | Support private accessors (getters and setters) |
v7.2.0 | Initial Release |
Example
class Counter extends HTMLElement {
#xValue = 0;
get #x() {
return this.#xValue;
}
set #x(value) {
this.#xValue = value;
window.requestAnimationFrame(this.#render.bind(this));
}
#clicked() {
this.#x++;
}
}
Installation
- npm
- Yarn
- pnpm
npm install @babel/plugin-transform-private-methods --save-dev
yarn add @babel/plugin-transform-private-methods --dev
pnpm add @babel/plugin-transform-private-methods --save-dev
Usage
With a configuration file (Recommended)
Without options:
{
"plugins": ["@babel/plugin-transform-private-methods"]
}
With options:
{
"plugins": [["@babel/plugin-transform-private-methods", { "loose": true }]]
}
Via CLI
$ babel --plugins @babel/plugin-transform-private-methods script.js
Via Node API
require("@babel/core").transformSync("code", {
plugins: ["@babel/plugin-transform-private-methods"],
});
Options
loose
boolean
, defaults to false
.
The loose
mode configuration setting must be the same as @babel/plugin-transform-class-properties
.
When true, private methods will be assigned directly on its parent
via Object.defineProperty
rather than a WeakSet
. This results in improved
performance and debugging (normal property access vs .get()
) at the expense
of potentially leaking "privates" via things like Object.getOwnPropertyNames
.
Consider migrating to the top level privateFieldsAsProperties
assumption.
{
"assumptions": {
"privateFieldsAsProperties": true,
"setPublicClassFields": true
}
}
Note that both privateFieldsAsProperties
and setPublicClassFields
must be set to true
.
Let's use the following as an example:
class Foo {
constructor() {
this.publicField = this.#privateMethod();
}
#privateMethod() {
return 42;
}
}
By default, this becomes:
var Foo = function Foo() {
"use strict";
babelHelpers.classCallCheck(this, Foo);
_privateMethod.add(this);
this.publicField = babelHelpers
.classPrivateMethodGet(this, _privateMethod, _privateMethod2)
.call(this);
};
var _privateMethod = new WeakSet();
var _privateMethod2 = function _privateMethod2() {
return 42;
};
With { privateFieldsAsProperties: true }
, it becomes:
var Foo = function Foo() {
"use strict";
babelHelpers.classCallCheck(this, Foo);
Object.defineProperty(this, _privateMethod, {
value: _privateMethod2,
});
this.publicField = babelHelpers
.classPrivateFieldLooseBase(this, _privateMethod)
[_privateMethod]();
};
var _privateMethod = babelHelpers.classPrivateFieldLooseKey("privateMethod");
var _privateMethod2 = function _privateMethod2() {
return 42;
};
You can read more about configuring plugin options here