johnnystefan/pattern-command

Skill: Implement Command Pattern

Purpose

Turns a request into a stand-alone object that contains all information about the request. This allows for parameterizing methods, queuing requests, and supporting undoable operations.

Procedural Instructions

1. Declare Command Interface: Define a single execution method, usually execute().
2. Create Concrete Commands: Map UI elements or triggers to specific business logic (Receivers). Store parameters within the command object.
3. Define Senders (Invokers): Senders should trigger the command without knowing what the command does or who the receiver is.
4. Setup Receiver: The class that actually knows how to perform the operation.

TypeScript Example

interface Command {
  execute(): void;
}

class Light {
  // Receiver
  turnOn() {
    console.log('Light is ON');
  }
}

class TurnOnCommand implements Command {
  constructor(private light: Light) {}
  execute() {
    this.light.turnOn();
  }
}

class RemoteControl {
  // Invoker
  private command!: Command;
  setCommand(c: Command) {
    this.command = c;
  }
  pressButton() {
    this.command.execute();
  }
}

Payoff

• Undo/Redo: Commands can store state snapshots to reverse operations.
• SRP: Decouples the object that invokes the operation from the one that knows how to perform it.