Factory Pattern

Definition

A creational design pattern that uses a 'Factory' method/function to create and return new objects without exposing the exact class or constructor logic to the client.

Explain Like I'm New

Imagine you are at a car dealership. You don't need to know how to weld metal or install an engine to get a car. You just tell the dealer 'I want a red SUV', and they build it and hand you the keys. The Factory Pattern is that dealer. It takes simple configuration and spits out complex, fully-formed objects.

Real World Example

Creating different types of Enemies in a game (Orc, Goblin, Dragon). Instead of importing 3 different Classes across your entire codebase, you just call `EnemyFactory.create('goblin')`.

Common Use Cases

•When object creation logic is complex
•When you need to create different objects sharing a common interface based on conditions

Interactive Example

class Developer { constructor(name) { this.name = name; this.type = "Dev"; } }
class Designer { constructor(name) { this.name = name; this.type = "Designer"; } }

// The Factory
class EmployeeFactory {
  create(name, type) {
    switch(type) {
      case "dev": return new Developer(name);
      case "designer": return new Designer(name);
      default: throw new Error("Unknown Employee Type");
    }
  }
}

const factory = new EmployeeFactory();
const employees = [];

// Clean, simple creation logic without needing to import specific classes everywhere
employees.push(factory.create("Alice", "dev"));
employees.push(factory.create("Bob", "designer"));

Interview Questions

basic

Why use a Factory instead of the `new` keyword directly?

intermediate

How does the Factory pattern relate to polymorphism?

advanced

What is an Abstract Factory?

Flash Cards

Question

Why use a Factory instead of `new`?

Click to reveal answer

Answer

If the object creation process requires API calls, reading config files, or complex `if/else` logic, putting all that in every file that needs the object causes massive code duplication. A Factory centralizes the creation logic.

Question

What is an Abstract Factory?

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Answer

A Factory that produces Factories. For example, a `UIFactory` that returns either a `MacUIFactory` or a `WinUIFactory` depending on the OS. Then, the specific factory handles creating buttons and windows for that OS.