JavaScript - Classes & Static Methods

Overview

Estimated time: 35–45 minutes

Classes provide a declarative syntax for prototype-based inheritance. Add instance methods, static methods, and fields (including private # fields).

Learning Objectives

• Define classes with constructors, instance methods, and static methods.
• Use public fields and private # fields.
• Understand that classes are not hoisted like function declarations.

Prerequisites

• JavaScript - Prototypes & Native Prototypes

Class basics

class Counter {
  #count = 0;                 // private field
  constructor(start = 0){ this.#count = start; }
  inc(){ this.#count++; }
  get value(){ return this.#count; } // accessor
  static from(counter){           // static factory
    const c = new Counter();
    c.#count = counter.value;
    return c;
  }
}
const c = new Counter(1); c.inc(); c.value; // 2

Common Pitfalls

• Classes are not hoisted for usage before declaration; define before use.
• Private # fields are truly private; they cannot be accessed via bracket syntax.