Private methods in Javascript classes

If you want to define a private property or method in a javascript class, you can define it by prepending a # sign in front:

class ClassWithPrivate {
  #privateField;
  #privateFieldWithInitializer = 42;

  #privateMethod() {
    // …
  }
}

In this way both the private properties and methods are not accessible from outside the body of the javascript class.

Mozilla documentation has a lot of more information about this.