The handler.getOwnPropertyDescriptor()
method is a trap for Object.getOwnPropertyDescriptor()
.
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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 (ECMA-262) The definition of '[[GetOwnProperty]]' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
getOwnPropertyDescriptor | Chrome Full support 49 | Edge Full support 12 | Firefox Full support 18 | IE No support No | Opera Full support 36 | Safari Full support 10 | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 18 | Opera Android Full support 36 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
Legend
- Full support
- Full support
- No support
- No support