代理模式

• 定义：为其他对象提供一种代理以控制对这个对象的访问

interface Subject {
    request(): void;
}

class RealSubject implements Subject {
    public request(): void {
        console.log('RealSubject: Handling request.');
    }
}
class Proxy implements Subject {
    private realSubject: RealSubject;

    /**
     * The Proxy maintains a reference to an object of the RealSubject class. It
     * can be either lazy-loaded or passed to the Proxy by the client.
     */
    constructor(realSubject: RealSubject) {
        this.realSubject = realSubject;
    }

    /**
     * The most common applications of the Proxy pattern are lazy loading,
     * caching, controlling the access, logging, etc. A Proxy can perform one of
     * these things and then, depending on the result, pass the execution to the
     * same method in a linked RealSubject object.
     */
    public request(): void {
        if (this.checkAccess()) {
            this.realSubject.request();
            this.logAccess();
        }
    }

    private checkAccess(): boolean {
        // Some real checks should go here.
        console.log('Proxy: Checking access prior to firing a real request.');

        return true;
    }

    private logAccess(): void {
        console.log('Proxy: Logging the time of request.');
    }
}
// 使用
function clientCode(subject: Subject) {
    // ...

    subject.request();

    // ...
}
const realSubject = new RealSubject();
const proxy = new Proxy(realSubject);
clientCode(proxy);