The handler.getOwnPropertyDescriptor()
method is a trap for the [[GetOwnProperty]]
object internal method, which is used by operations such as Object.getOwnPropertyDescriptor()
.
The handler.getOwnPropertyDescriptor()
method is a trap for the [[GetOwnProperty]]
object internal method, which is used by operations such as Object.getOwnPropertyDescriptor()
.
new Proxy(target, { getOwnPropertyDescriptor(target, prop) { } });
The getOwnPropertyDescriptor()
method must return an object or undefined
.
This trap can intercept these operations:
Or any other operation that invokes the [[GetOwnProperty]]
internal method.
If the following invariants are violated, the trap throws a TypeError
when invoked.
getOwnPropertyDescriptor()
must return an object or undefined
.Object.getOwnPropertyDescriptor(target)
can be applied to the target object using Object.defineProperty()
and will not throw an exception.The following code traps Object.getOwnPropertyDescriptor()
.
const p = new Proxy( { a: 20 }, { getOwnPropertyDescriptor(target, prop) { console.log(`called: ${prop}`); return { configurable: true, enumerable: true, value: 10 }; }, }, ); console.log(Object.getOwnPropertyDescriptor(p, "a").value); // "called: a" // 10
The following code violates an invariant.
const obj = { a: 10 }; Object.preventExtensions(obj); const p = new Proxy(obj, { getOwnPropertyDescriptor(target, prop) { return undefined; }, }); Object.getOwnPropertyDescriptor(p, "a"); // TypeError is thrown
Specification |
---|
ECMAScript Language Specification # sec-proxy-object-internal-methods-and-internal-slots-getownproperty-p |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
getOwnPropertyDescriptor |
49 | 12 | 18 | 36 | 10 | 49 | 18 | 36 | 10 | 5.0 | 49 | 1.0 | 6.0.0 |
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/getOwnPropertyDescriptor