handler.getOwnPropertyDescriptor()
The handler.getOwnPropertyDescriptor()
method is a trap for Object.getOwnPropertyDescriptor()
.
Syntax
const p = new Proxy(target, { getOwnPropertyDescriptor: function(target, prop) { } });
Parameters
The following parameters are passed to the getOwnPropertyDescriptor()
method. this
is bound to the handler.
target
-
The target object.
prop
-
The name of the property whose description should be retrieved.
Return value
The getOwnPropertyDescriptor()
method must return an object or undefined
.
Description
The handler.getOwnPropertyDescriptor()
method is a trap for Object.getOwnPropertyDescriptor()
.
Interceptions
This trap can intercept these operations:
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
-
getOwnPropertyDescriptor()
must return an object orundefined
. - A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as non-existent, if it exists as an own property of the target object and the target object is not extensible.
- A property cannot be reported as existent, if it does not exists as an own property of the target object and the target object is not extensible.
- A property cannot be reported as non-configurable, if it does not exists as an own property of the target object or if it exists as a configurable own property of the target object.
- The result of
Object.getOwnPropertyDescriptor(target)
can be applied to the target object usingObject.defineProperty()
and will not throw an exception.
Examples
Trapping of getOwnPropertyDescriptor
The following code traps Object.getOwnPropertyDescriptor()
.
const p = new Proxy({ a: 20}, { getOwnPropertyDescriptor: function(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: function(target, prop) { return undefined; } }); Object.getOwnPropertyDescriptor(p, 'a'); // TypeError is thrown
Specifications
Specification |
---|
ECMAScript Language Specification (ECMAScript) # sec-proxy-object-internal-methods-and-internal-slots-getownproperty-p |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
getOwnPropertyDescriptor |
49 |
12 |
18 |
No |
36 |
10 |
49 |
49 |
18 |
36 |
10 |
5.0 |
See also
© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/getOwnPropertyDescriptor