no-private-class-fields.md

no-private-class-fields

This prevents the use of Private Class Fields

class Foo {
  static #bar = 1
  #bar = 1

  isFoo() {
    return #bar === 1
  }
}

These will not be allowed because they are not supported in the following browsers:

• Edge < 79
• Safari < 14.1
• Firefox < 90
• Chrome < 74

What is the Fix?

Use of a WeakMap will cover most use cases:

const fooPrivateState = new WeakMap()

class Foo {
  constructor() {
    fooPrivateState.set(this, { bar: 1 })
  }

  isFoo() {
    return (fooPrivateState.get(this) || {}).bar === 1
  }
}

This can be safely disabled if you intend to compile code with the @babel/plugin-transform-private-property-in-object Babel plugin, or @babel/preset-env.