How to Make Static Fields Private in a JavaScript Class?

Starting with ES13/ES2022, you can make static fields/members in a class private by prefixing the field name with # (hash symbol).

For example:

// ES13+
class Foo {
    static PUBLIC_PROP = 321;
    static #PRIVATE_PROP = 123;

console.log(Foo.PUBLIC_PROP); // 321

// SyntaxError

Private static fields are only accessible on:

  • On the class itself (e.g. MyClass.staticField), and;
  • When using this in static methods.

One important limitation to understand is that, if a static method in a base class accesses a private static field (or method) within that class using the this context, and you try to access this method from a subclass, a TypeError will be thrown:

class BaseClass {

    static baseStaticMethod1() {
        BaseClass.#PRIVATE_STATIC_FIELD = 'foo';
        return BaseClass.#PRIVATE_STATIC_FIELD;

    static baseStaticMethod2() {
        this.#PRIVATE_STATIC_FIELD = 'foo';
        return this.#PRIVATE_STATIC_FIELD;

class SubClass extends BaseClass {}

console.log(SubClass.baseStaticMethod1()); // 'foo'

// TypeError: Cannot write private member #PRIVATE_STATIC_FIELD to an object whose class did not declare it

In addition to declaring static fields as private, you can also:

This post was published (and was last revised ) by Daniyal Hamid. Daniyal currently works as the Head of Engineering in Germany and has 20+ years of experience in software engineering, design and marketing. Please show your love and support by sharing this post.