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---
id: babel-plugin-proposal-private-methods
title: @babel/plugin-proposal-private-methods
sidebar_label: private-methods
---
NOTE: This plugin is included in
@babel/preset-env
History
| Version | Changes | | --- | --- | | `v7.3.0` | Support private accessors (getters and setters) | | `v7.2.0` | Initial Release |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++;
}
}
$ npm install @babel/plugin-proposal-private-methods --save-dev
Without options:
{
"plugins": ["@babel/plugin-proposal-private-methods"]
}
With options:
{
"plugins": [["@babel/plugin-proposal-private-methods", { "loose": true }]]
}
$ babel --plugins @babel/plugin-proposal-private-methods script.js
require("@babel/core").transformSync("code", {
plugins: ["@babel/plugin-proposal-private-methods"],
});
boolean
, defaults to false
.
Note: The
loose
mode configuration setting must be the same as@babel/plugin-proposal-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
.
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 { loose: 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