إنشاء Proxy

ما هو Proxy؟

معالج فارغ

const target = { greeting: 'hello' };
const proxy = new Proxy(target, {});

console.log(proxy.greeting);
proxy.greeting = 'hi';
console.log(target.greeting);

يشترك الكائن الهدف وProxy في الحالة

const target = { count: 0 };
const proxy = new Proxy(target, {});

proxy.count = 5;
console.log(target.count);
target.count = 10;
console.log(proxy.count);

إضافة اعتراض get

const proxy = new Proxy({ name: 'Ada' }, {
  get(target, prop) {
    console.log('reading ' + prop);
    return target[prop];
  }
});

console.log(proxy.name);

معاملات الاعتراض

const proxy = new Proxy({ a: 1 }, {
  get(target, prop) {
    return prop in target ? target[prop] : 'missing';
  }
});

console.log(proxy.a);
console.log(proxy.b);

خصائص محسوبة عند القراءة

const proxy = new Proxy({ first: 'Ada', last: 'Lovelace' }, {
  get(target, prop) {
    if (prop === 'full') return target.first + ' ' + target.last;
    return target[prop];
  }
});

console.log(proxy.full);

إضافة اعتراض set

const proxy = new Proxy({}, {
  set(target, prop, value) {
    console.log('setting ' + prop + ' = ' + value);
    target[prop] = value;
    return true;
  }
});

proxy.score = 42;
console.log(proxy.score);

اعتراض has

const proxy = new Proxy({ a: 1 }, {
  has(target, prop) {
    console.log('checking ' + prop);
    return prop in target;
  }
});

console.log('a' in proxy);
console.log('b' in proxy);

اعتراض deleteProperty

const proxy = new Proxy({ secret: 'x', ok: 'y' }, {
  deleteProperty(target, prop) {
    console.log('deleting ' + prop);
    delete target[prop];
    return true;
  }
});

delete proxy.secret;
console.log(Object.keys(proxy));

اعتراضات كثيرة متاحة

const proxy = new Proxy({ x: 1, y: 2 }, {
  ownKeys(target) {
    console.log('listing keys');
    return Object.keys(target);
  }
});

console.log(Object.keys(proxy));

لماذا تهم Proxies

const logged = new Proxy({ v: 0 }, {
  get: (t, p) => { console.log('get ' + p); return t[p]; },
  set: (t, p, val) => { console.log('set ' + p); t[p] = val; return true; }
});
logged.v = 9;
console.log(logged.v);

تحقق سريع

مراجعة: إنشاء Proxy