The handler.defineProperty()
method is a trap for Object.defineProperty()
.
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Syntax
const p = new Proxy(target, { defineProperty: function(target, property, descriptor) { } });
Parameters
The following parameters are passed to the defineProperty()
method. this
is bound to the handler.
target
- The target object.
property
- The name or
Symbol
of the property whose description is to be retrieved. descriptor
- The descriptor for the property being defined or modified.
Return value
The defineProperty()
method must return a Boolean
indicating whether or not the property has been successfully defined.
Description
The handler.defineProperty()
method is a trap for Object.defineProperty()
.
Interceptions
This trap can intercept these operations:
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
- A property cannot be added, if the target object is not extensible.
- A property cannot be added as or modified to be non-configurable, if it does not exists as a non-configurable own property of the target object.
- A property may not be non-configurable, if a corresponding configurable property of the target object exists.
- If a property has a corresponding target object property then
Object.defineProperty(target, prop, descriptor)
will not throw an exception. - In strict mode, a
false
return value from thedefineProperty()
handler will throw aTypeError
exception.
Examples
Trapping of defineProperty
The following code traps Object.defineProperty()
.
const p = new Proxy({}, { defineProperty: function(target, prop, descriptor) { console.log('called: ' + prop); return true; } }); const desc = { configurable: true, enumerable: true, value: 10 }; Object.defineProperty(p, 'a', desc); // "called: a"
When calling Object.defineProperty()
or Reflect.defineProperty()
, the descriptor
passed to defineProperty()
trap has one restriction—only following properties are usable (non-standard properties will be ignored):
enumerable
configurable
writable
value
get
set
const p = new Proxy({}, { defineProperty(target, prop, descriptor) { console.log(descriptor); return Reflect.defineProperty(target, prop, descriptor); } }); Object.defineProperty(p, 'name', { value: 'proxy', type: 'custom' }); // { value: 'proxy' }
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of '[[DefineOwnProperty]]' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
defineProperty | 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