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Proxy .

const handler = {
  get(target, name) {
    return name in target ? target[name] : 42;
  },
};

const p = new Proxy({}, handler);
p.a = 1;
console.log(p.a, p.b); // 1, 42

Proxy target( ) get handler . undefined 42 .

Proxy .

handler: .
traps: . ( '' .)
target: . . ( ) target .
invariants: '' . TypeError .

Proxy . .

/
`handler.getPrototypeOf()`	`Object.getPrototypeOf()` `Reflect.getPrototypeOf()` `__proto__` `Object.prototype.isPrototypeOf()` `instanceof`
`handler.setPrototypeOf()`	`Object.setPrototypeOf()` `Reflect.setPrototypeOf()`
`handler.isExtensible()`	`Object.isExtensible()` `Reflect.isExtensible()`
`handler.preventExtensions()`	`Object.preventExtensions()` `Reflect.preventExtensions()`
`handler.getOwnPropertyDescriptor()`	`Object.getOwnPropertyDescriptor()` `Reflect.getOwnPropertyDescriptor()`
`handler.defineProperty()`	`Object.defineProperty()` `Reflect.defineProperty()`
`handler.has()`	`foo in proxy` `foo in Object.create(proxy)` `Reflect.has()`
`handler.get()`	`proxy[foo]` `proxy.bar` `Object.create(proxy)[foo]` `Reflect.get()`
`handler.set()`	`proxy[foo] = bar` `proxy.foo = bar` `Object.create(proxy)[foo] = bar` `Reflect.set()`
`handler.deleteProperty()`	`delete proxy[foo]` `delete proxy.foo` `Reflect.deleteProperty()`
`handler.ownKeys()`	`Object.getOwnPropertyNames()` `Object.getOwnPropertySymbols()` `Object.keys()` `Reflect.ownKeys()`
`handler.apply()`	`proxy(..args)` `Function.prototype.apply()` `Function.prototype.call()` `Reflect.apply()`
`handler.construct()`	`new proxy(...args)` `Reflect.construct()`

`Proxy`

Proxy.revocable() Proxy . revoke .

TypeError .

const revocable = Proxy.revocable(
  {},
  {
    get(target, name) {
      return `[[${name}]]`;
    },
  },
);
const proxy = revocable.proxy;
console.log(proxy.foo); // "[[foo]]"

revocable.revoke();

console.log(proxy.foo); // TypeError:   'get'   
proxy.foo = 1; // TypeError:   'set'   
delete proxy.foo; // TypeError:   'deleteProperty'   
console.log(typeof proxy); // "object", typeof

(Reflection)

Reflect . .

Reflect .

Reflect target .

, Reflect.has() in :

Reflect.has(Object, "assign"); // true

apply()

Reflect , this ( ) arguments Function.prototype.apply() .

Function.prototype.apply.call(Math.floor, undefined, [1.75]);

Reflect.apply .

Reflect.apply(Math.floor, undefined, [1.75]);
// 1

Reflect.apply(String.fromCharCode, undefined, [104, 101, 108, 108, 111]);
// "hello"

Reflect.apply(RegExp.prototype.exec, /ab/, ["confabulation"]).index;
// 4

Reflect.apply("".charAt, "ponies", [3]);
// "i"

Object.defineProperty , TypeError . try...catch . , Reflect.defineProperty() , if...else :

if (Reflect.defineProperty(target, property, attributes)) {
  // 
} else {
  // 
}

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This page was last modified on 2026 7 15 by MDN contributors.

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