Patternalysis

Construct complex objects step-by-step without constructor parameter explosion and confusion.

What is it?

The Builder pattern lets you construct complex objects step-by-step using clear, readable method calls instead of confusing constructors with many parameters.

Interactive Demo: Builder vs Constructor Parameter Explosion

Build a custom computer. See how Builder stays clear while constructor parameters become unmanageable:

🔧 Builder Pattern

Build Process:

Click buttons above to configure computer...

💥 Constructor Parameters

Constructor requires:
CPU, RAM, Storage, GPU, Motherboard, PSU, Cooling, Case
Easy to mess up the order!

Constructor Calls:

Click buttons above to simulate constructor calls...

💡 Key Insight:

• Builder Pattern: Clear method names, any order, impossible to confuse parameters!
• Constructor: 8+ parameters in exact order, easy to swap and create bugs!
• Real Impact: Builder prevents configuration errors, constructor creates maintenance nightmares

Code Example

class ComputerBuilder {
  private computer: Partial<ComputerSpecs> = {};

  setCPU(cpu: string): ComputerBuilder {
    this.computer.cpu = cpu;
    return this; // Method chaining
  }

  setRAM(ram: string): ComputerBuilder {
    this.computer.ram = ram;
    return this;
  }

  setGPU(gpu: string): ComputerBuilder {
    this.computer.gpu = gpu;
    return this;
  }

  build(): Computer {
    return new Computer(this.computer);
  }
}

// Usage - Clear and readable
const computer = new ComputerBuilder()
  .setCPU("Intel i9-13900K")     // Clear what each parameter is
  .setRAM("32GB DDR5")           // Any order you want
  .setGPU("RTX 4090")            // Self-documenting
  .build();

// vs Constructor Approach - Confusing and error-prone
const computer2 = new Computer(
  "Intel i9-13900K",  // What is this parameter?
  "32GB DDR5",        // What order should these be in?
  "1TB SSD",          // Easy to swap these accidentally
  "RTX 4090",         // Which one is GPU vs Storage?
  "Z790 Extreme",     // Did I get the order right?
  "1000W Platinum",   // Getting confusing...
  "AIO Liquid",       // Too many parameters!
  "Gaming ATX"        // Wrong order = Wrong computer!
);

Common Uses

Configuration objects (database connections, API clients)
Complex UI components with many optional properties
SQL query builders and fluent APIs
Form builders and validation setup
Test data builders and mock object creation
HTTP request builders (headers, params, body)

When to Use

When constructors would have many parameters (4+ parameters)
When you need optional or default values for complex objects
When parameter order could cause confusion or bugs
When you want to create different variations of the same object
When you need to validate or transform data during construction

Caution

Adds complexity for simple objects (use regular constructors for 1-3 params)
Requires more classes and methods than direct construction
May be slower than direct construction (usually negligible)
Team needs to understand the pattern to use effectively