JavaScript Static Members

Class members marked static belong to the class itself — not to any instance. You call them via the class name.

class MathUtil {
  static add(a, b) {
    return a + b;
  }
  static multiply(a, b) {
    return a * b;
  }
}

console.log(MathUtil.add(2, 3));      // 5
console.log(MathUtil.multiply(4, 5)); // 20

// const m = new MathUtil();
// m.add(2, 3);  // TypeError — add is not on the instance

Static methods don’t have access to instance this (there’s no instance involved). They’re plain functions namespaced under a class.

Static Fields

You can attach data to the class too — useful for constants or configuration.

class HttpClient {
  static defaultTimeout = 5000;
  static maxRetries = 3;
}

console.log(HttpClient.defaultTimeout); // 5000
HttpClient.defaultTimeout = 10000;       // mutable unless you Object.freeze
console.log(HttpClient.defaultTimeout); // 10000

A Classic Use: Factory Methods

A static method that returns a new instance is called a factory method. Useful when there are multiple ways to construct an object.

class User {
  constructor(name, role) {
    this.name = name;
    this.role = role;
  }

  static makeAdmin(name) {
    return new User(name, "admin");
  }

  static makeGuest() {
    return new User("Guest", "guest");
  }
}

const ada = User.makeAdmin("Ada");
const g = User.makeGuest();
console.log(ada);  // User { name: 'Ada', role: 'admin' }
console.log(g);    // User { name: 'Guest', role: 'guest' }

Static Methods on Built-ins

You’ve used static methods on built-in classes all along:

• “Math.max(...), Math.random() — static on Math.”
• Object.keys(obj), Object.entries(obj) — static on Object.
• Array.isArray(x), Array.from(x) — static on Array.
• Number.isFinite(x) — static on Number.

These all illustrate the pattern — class-level utilities that don’t need an instance.

When to Use Static

• Factory methods (User.makeGuest()).
• Utility functions that don’t depend on instance state.
• Class-level constants and configuration.
• Type guards / branding helpers (like the private-field in check).

Don’t put everything static — if a method operates on instance state, it should be an instance method.

Up Next

Properties that look like data but actually run a function — getters and setters.