The handler.set()
method is a trap for setting a property value.
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Syntax
const p = new Proxy(target, { set: function(target, property, value, receiver) { } });
Parameters
The following parameters are passed to the set()
method. this
is bound to the handler.
target
- The target object.
property
- The name or
Symbol
of the property to set. value
- The new value of the property to set.
receiver
-
The object to which the assignment was originally directed. This is usually the proxy itself. But a
set()
handler can also be called indirectly, via the prototype chain or various other ways.For example: Suppose a script does
obj.name = "jen"
, andobj
is not a proxy, and has no own property.name
, but it has a proxy on its prototype chain. That proxy'sset()
handler will be called, andobj
will be passed as the receiver.
Return value
The set()
method should return a boolean value.
- Return
true
to indicate that assignment succeeded. - If the
set()
method returnsfalse
, and the assignment happened in strict-mode code, aTypeError
will be thrown.
Description
The handler.set()
method is a trap for setting property value.
Interceptions
This trap can intercept these operations:
- Property assignment:
proxy[foo] = bar
andproxy.foo = bar
- Inherited property assignment:
Object.create(proxy)[foo] = bar
Reflect.set()
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
- Cannot change the value of a property to be different from the value of the corresponding target object property if the corresponding target object property is a non-writable, non-configurable data property.
- Cannot set the value of a property if the corresponding target object property is a non-configurable accessor property that has
undefined
as its[[Set]]
attribute. - In strict mode, a
false
return value from theset()
handler will throw aTypeError
exception.
Examples
Trap setting of a property value
The following code traps setting a property value.
const p = new Proxy({}, { set: function(target, prop, value, receiver) { target[prop] = value; console.log('property set: ' + prop + ' = ' + value); return true; } }) console.log('a' in p); // false p.a = 10; // "property set: a = 10" console.log('a' in p); // true console.log(p.a); // 10
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of '[[Set]]' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
set | 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