Builder

Telescoping constructor / boolean soup

Every optional ingredient becomes another positional argument. The call site is a wall of unlabeled booleans — nobody can tell what they mean without opening the class.

class Burger {
  constructor(size, cheese, bacon,
              lettuce, egg, spicy, patties) { /* … */ }
}

// which true/false is which?? 🤯
new Burger('L', true, false, true, true, false, 2);

A fluent builder assembles the product

Each add…() records one choice and returns this, so calls chain. build() hands back the finished object at the end.

class BurgerBuilder {
  constructor() { this.parts = []; }

  addCheese() { this.parts.push('cheese'); return this; }
  addBacon()  { this.parts.push('bacon');  return this; }

  build()     { return new Burger(this.parts); }
}

new BurgerBuilder().addCheese().addBacon().build();

Pick toppings — watch the chain build itself

Click ingredients to call the matching add…(). Then call build() to get the finished burger.

new BurgerBuilder()

Step-by-step construction, readable call sites

• Builds a complex object incrementally — one clearly-named call per option.
• Readable call sites: .addCheese().addBacon().build() beats seven positional booleans.
• Great when there are many optional parameters; the product can even come out immutable once build() runs.
• vs. Factory: a Factory picks which type to create; a Builder assembles the pieces of one complex object.
• Caution: overkill for objects with just 1–2 fields — a plain constructor is fine.