The handler.defineProperty()
method is a trap for Object.defineProperty()
.
Syntax
var 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 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 it has successfully defined the property on the target or not.
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
The following code traps Object.defineProperty()
.
var p = new Proxy({}, { defineProperty: function(target, prop, descriptor) { console.log("called: " + prop); return true; } }); var desc = { configurable: true, enumerable: true, value: 10 }; Object.defineProperty(p, "a", desc); // "called: a"
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of '[[DefineOwnProperty]]' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of '[[DefineOwnProperty]]' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | ? | 18 (18) | ? | ? | ? |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | ? | ? | 18.0 (18) | ? | ? | ? |