The handler.getPrototypeOf() method is a trap for the [[GetPrototypeOf]] object internal method, which is used by operations such as Object.getPrototypeOf().
const monster = {
eyeCount: 4,
};
const monsterPrototype = {
eyeCount: 2,
};
const handler = {
getPrototypeOf(target) {
return monsterPrototype;
},
};
const proxy = new Proxy(monster, handler);
console.log(Object.getPrototypeOf(proxy) === monsterPrototype);
// Expected output: true
console.log(Object.getPrototypeOf(proxy).eyeCount);
// Expected output: 2new Proxy(target, {
getPrototypeOf(target) {
}
})The following parameter is passed to the getPrototypeOf() method. this is bound to the handler.
targetThe target object.
The getPrototypeOf() method must return an object or null, representing the prototype of the target object.
This trap can intercept these operations:
Or any other operation that invokes the [[GetPrototypeOf]] internal method.
The proxy's [[GetPrototypeOf]] internal method throws a TypeError if the handler definition violates one of the following invariants:
Object or null.Reflect.isExtensible() returns false on target), the result must be the same as the result of Reflect.getPrototypeOf(target).const obj = {};
const proto = {};
const handler = {
getPrototypeOf(target) {
console.log(target === obj); // true
console.log(this === handler); // true
return proto;
},
};
const p = new Proxy(obj, handler);
console.log(Object.getPrototypeOf(p) === proto); // trueconst obj = {};
const p = new Proxy(obj, {
getPrototypeOf(target) {
return Array.prototype;
},
});
console.log(
Object.getPrototypeOf(p) === Array.prototype, // true
Reflect.getPrototypeOf(p) === Array.prototype, // true
p.__proto__ === Array.prototype, // true
Array.prototype.isPrototypeOf(p), // true
p instanceof Array, // true
);const obj = {};
const p = new Proxy(obj, {
getPrototypeOf(target) {
return "foo";
},
});
Object.getPrototypeOf(p); // TypeError: "foo" is not an object or null
const obj2 = Object.preventExtensions({});
const p2 = new Proxy(obj2, {
getPrototypeOf(target) {
return {};
},
});
Object.getPrototypeOf(p2); // TypeError: expected same prototype value