CODESAMPLE

Command - JavaScript

Command JavaScript

The Command pattern encapsulates a request as an object, allowing parameterization of clients with different requests, queue or log requests, and support undoable operations. This implementation uses a simple Command interface with an execute method. Concrete commands (like AddCommand, SubtractCommand) implement this interface, holding the necessary data to perform the operation. An Invoker (Calculator) takes and stores commands, delegating execution to them. This is idiomatic JavaScript by leveraging its flexible object and function-as-first-class-citizen nature. The use of functions as command objects simplifies the code and avoids the need for complex class hierarchies often seen in statically-typed languages.

// Command Interface
class Command {
  constructor(receiver, action, operand) {
    this.receiver = receiver;
    this.action = action;
    this.operand = operand;
  }

  execute() {
    this.receiver[this.action](this.operand);
  }
}

// Receiver
class Calculator {
  constructor() {
    this.value = 0;
  }

  add(operand) {
    this.value += operand;
    console.log(`Added ${operand}, value is now ${this.value}`);
  }

  subtract(operand) {
    this.value -= operand;
    console.log(`Subtracted ${operand}, value is now ${this.value}`);
  }

  getValue() {
    return this.value;
  }
}

// Invoker
class CommandInvoker {
  constructor() {
    this.commands = [];
  }

  addCommand(command) {
    this.commands.push(command);
  }

  executeCommands() {
    for (const command of this.commands) {
      command.execute();
    }
  }
}


// Usage
const calculator = new Calculator();
const invoker = new CommandInvoker();

const addCommand1 = new Command(calculator, 'add', 10);
const subtractCommand = new Command(calculator, 'subtract', 5);
const addCommand2 = new Command(calculator, 'add', 2);

invoker.addCommand(addCommand1);
invoker.addCommand(subtractCommand);
invoker.addCommand(addCommand2);

invoker.executeCommands();
console.log("Final value:", calculator.getValue());