class Command {
  constructor(execute, undo) {
    this.execute = execute;
    this.undo = undo;
  }
}

class CommandManager {
  constructor() {
    this.history = [];
  }

  execute(command) {
    command.execute();
    this.history.push(command);
  }

  undo() {
    const command = this.history.pop();
    if (command) command.undo();
  }
}

// Usage
const manager = new CommandManager();

const addChar = new Command(
  () => console.log('Added character'),
  () => console.log('Undo add character')
);

manager.execute(addChar);
manager.execute(addChar);
manager.undo(); // Undo add character