@babel/plugin-proposal-private-property-in-object
NOTE: This plugin is included in
@babel/preset-env
, in ES2022
Example
In
class Foo { #bar = "bar"; test(obj) { return #bar in obj; } }
Out
class Foo { constructor() { _bar.set(this, { writable: true, value: "bar", }); } test() { return _bar.has(this); } } var _bar = new WeakMap();
Installation
npm install --save-dev @babel/plugin-proposal-private-property-in-object
Usage
With a configuration file (Recommended)
{ "plugins": ["@babel/plugin-proposal-private-property-in-object"] }
Via CLI
babel --plugins @babel/plugin-proposal-private-property-in-object
Via Node API
require("@babel/core").transformSync("code", { plugins: ["@babel/plugin-proposal-private-property-in-object"], });
Options
loose
boolean
, defaults to false
.
Note: The
loose
mode configuration setting must be the same as@babel/proposal-class-properties
.
When true, private property in
expressions will check own properties (as opposed to inherited ones) on the object, instead of checking for presence inside 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.
// babel.config.json { "assumptions": { "privateFieldsAsProperties": true, "setPublicClassFields": true } }
Note that both privateFieldsAsProperties
and setPublicClassFields
must be set to true
.
Example
In
class Foo { #bar = "bar"; test(obj) { return #bar in obj; } }
Out
class Foo { constructor() { Object.defineProperty(this, _bar, { writable: true, value: "bar", }); } test() { return Object.prototype.hasOwnProperty.call(this, _bar); } } var _bar = babelHelpers.classPrivateFieldLooseKey("bar");
You can read more about configuring plugin options here