TypeScript 命令模式讲解和代码示例

/** * 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(); 

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.)