How to Make Static Methods Private in a JavaScript Class?

Starting with ES13/ES2022, you can make any static class method private by prefixing the method name with # (hash symbol).

For example:

// ES13+
class Foo {
    static publicMethod() {
        return Foo.#privateMethod();
    }

    static #privateMethod() {
        return 'foobar';
    }
}

console.log(Foo.publicMethod()); // 'foobar'

// SyntaxError
console.log(Foo.#privateMethod);

Similarly, you can make static getter, setter, generator, async, or async generator methods private as well:

// ES13+
class MyClass {
    static #privateMethod() {}
    static * #privateGeneratorMethod() {}

    static async #privateAsyncMethod() {}
    static async * #privateAsyncGeneratorMethod() {}

    static get #privateGetter() {}
    static set #privateSetter(value) {}
}

Private static methods are only accessible:

• On the class itself (e.g. MyClass.staticMethod()), 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 method (or field) 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 #privateStaticMethod() {
        return 'foo';
    }

    static baseStaticMethod1() {
        return BaseClass.#privateStaticMethod();
    }

    static baseStaticMethod2() {
        return this.#privateStaticMethod();
    }
}

class SubClass extends BaseClass {}

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

// TypeError: Receiver must be class BaseClass
console.log(SubClass.baseStaticMethod2());

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

• Make static class fields private;
• Make class fields private;
• Make class methods private.