@babel/plugin-transform-private-property-in-object
info
This plugin is included in @babel/preset-env
, in ES2022
Example
In
JavaScript
class Foo {
#bar = "bar";
test(obj) {
return #bar in obj;
}
}
Out
JavaScript
class Foo {
constructor() {
_bar.set(this, {
writable: true,
value: "bar",
});
}
test() {
return _bar.has(this);
}
}
var _bar = new WeakMap();
Installation
- npm
- Yarn
- pnpm
npm install --save-dev @babel/plugin-transform-private-property-in-object
yarn add --dev @babel/plugin-transform-private-property-in-object
pnpm add --save-dev @babel/plugin-transform-private-property-in-object
Usage
With a configuration file (Recommended)
babel.config.json
{
"plugins": ["@babel/plugin-transform-private-property-in-object"]
}
Via CLI
Shell
babel --plugins @babel/plugin-transform-private-property-in-object
Via Node API
JavaScript
require("@babel/core").transformSync("code", {
plugins: ["@babel/plugin-transform-private-property-in-object"],
});
Options
loose
boolean
, defaults to false
.
note
The loose
mode configuration setting must be the same as @babel/transform-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
.
caution
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
JavaScript
class Foo {
#bar = "bar";
test(obj) {
return #bar in obj;
}
}
Out
JavaScript
class Foo {
constructor() {
Object.defineProperty(this, _bar, {
writable: true,
value: "bar",
});
}
test() {
return Object.prototype.hasOwnProperty.call(this, _bar);
}
}
var _bar = babelHelpers.classPrivateFieldLooseKey("bar");
tip
You can read more about configuring plugin options here