Command en TypeScript

Command es un patrón de diseño de comportamiento que convierte solicitudes u operaciones simples en objetos.

La conversión permite la ejecución diferida de comandos, el almacenamiento del historial de comandos, etc.

Complejidad:

Popularidad:

Ejemplos de uso: El patrón Command es muy común en el código TypeScript. La mayoría de las veces se utiliza como alternativa a las retrollamadas (callbacks) para parametrizar elementos UI con acciones. También se utiliza para poner tareas en cola, realizar el seguimiento del historial de operaciones, etc.

Identificación: El patrón Command es reconocible por los métodos de comportamiento en un tipo de clase abstracta/interfaz (emisora) que invoca un método en una implementación de un tipo de clase abstracta/interfaz diferente (receptora) que la implementación del comando ha implementado durante su creación. Las clases de comando se limitan normalmente a acciones específicas.

Ejemplo conceptual

Este ejemplo ilustra la estructura del patrón de diseño Command y se centra en las siguientes preguntas:

¿De qué clases se compone?
¿Qué papeles juegan esas clases?
¿De qué forma se relacionan los elementos del patrón?

index.ts: Ejemplo conceptual

/**
 * The Command interface declares a method for executing a command.
 */
interface Command {
    execute(): void;
}

/**
 * Some commands can implement simple operations on their own.
 */
class SimpleCommand implements Command {
    private payload: string;

    constructor(payload: string) {
        this.payload = payload;
    }

    public execute(): void {
        console.log(`SimpleCommand: See, I can do simple things like printing (${this.payload})`);
    }
}

/**
 * However, some commands can delegate more complex operations to other objects,
 * called "receivers."
 */
class ComplexCommand implements Command {
    private receiver: Receiver;

    /**
     * Context data, required for launching the receiver's methods.
     */
    private a: string;

    private b: string;

    /**
     * Complex commands can accept one or several receiver objects along with
     * any context data via the constructor.
     */
    constructor(receiver: Receiver, a: string, b: string) {
        this.receiver = receiver;
        this.a = a;
        this.b = b;
    }

    /**
     * Commands can delegate to any methods of a receiver.
     */
    public execute(): void {
        console.log('ComplexCommand: Complex stuff should be done by a receiver object.');
        this.receiver.doSomething(this.a);
        this.receiver.doSomethingElse(this.b);
    }
}

/**
 * The Receiver classes contain some important business logic. They know how to
 * perform all kinds of operations, associated with carrying out a request. In
 * fact, any class may serve as a Receiver.
 */
class Receiver {
    public doSomething(a: string): void {
        console.log(`Receiver: Working on (${a}.)`);
    }

    public doSomethingElse(b: string): void {
        console.log(`Receiver: Also working on (${b}.)`);
    }
}

/**
 * The Invoker is associated with one or several commands. It sends a request to
 * the command.
 */
class Invoker {
    private onStart: Command;

    private onFinish: Command;

    /**
     * Initialize commands.
     */
    public setOnStart(command: Command): void {
        this.onStart = command;
    }

    public setOnFinish(command: Command): void {
        this.onFinish = command;
    }

    /**
     * The Invoker does not depend on concrete command or receiver classes. The
     * Invoker passes a request to a receiver indirectly, by executing a
     * command.
     */
    public doSomethingImportant(): void {
        console.log('Invoker: Does anybody want something done before I begin?');
        if (this.isCommand(this.onStart)) {
            this.onStart.execute();
        }

        console.log('Invoker: ...doing something really important...');

        console.log('Invoker: Does anybody want something done after I finish?');
        if (this.isCommand(this.onFinish)) {
            this.onFinish.execute();
        }
    }

    private isCommand(object): object is Command {
        return object.execute !== undefined;
    }
}

/**
 * The client code can parameterize an invoker with any commands.
 */
const invoker = new Invoker();
invoker.setOnStart(new SimpleCommand('Say Hi!'));
const receiver = new Receiver();
invoker.setOnFinish(new ComplexCommand(receiver, 'Send email', 'Save report'));

invoker.doSomethingImportant();

Output.txt: Resultado de la ejecución

Invoker: Does anybody want something done before I begin?
SimpleCommand: See, I can do simple things like printing (Say Hi!)
Invoker: ...doing something really important...
Invoker: Does anybody want something done after I finish?
ComplexCommand: Complex stuff should be done by a receiver object.
Receiver: Working on (Send email.)
Receiver: Also working on (Save report.)

Command en TypeScript

Ejemplo conceptual

index.ts: Ejemplo conceptual

Output.txt: Resultado de la ejecución

Command en otros lenguajes