The handler.construct()
method is a trap for the new
operator. In order for the new operation to be valid on the resulting Proxy object, the target used to initialize the proxy must itself have a [[Construct]]
internal method (i.e. new target
must be valid).
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Syntax
const p = new Proxy(target, { construct: function(target, argumentsList, newTarget) { } });
Parameters
The following parameters are passed to the construct()
method. this
is bound to the handler.
target
- The target object.
argumentsList
- The list of arguments for the constructor.
newTarget
- The constructor that was originally called,
p
above.
Return value
The construct
method must return an object.
Description
The handler.construct()
method is a trap for the new
operator.
Interceptions
This trap can intercept these operations:
new Proxy(...args)
Reflect.construct()
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
- The result must be an
Object
.
Examples
Trapping the new operator
The following code traps the new
operator.
const p = new Proxy(function() {}, { construct: function(target, argumentsList, newTarget) { console.log('called: ' + argumentsList.join(', ')); return { value: argumentsList[0] * 10 }; } }); console.log(new p(1).value); // "called: 1" // 10
The following code violates the invariant.
const p = new Proxy(function() {}, { construct: function(target, argumentsList, newTarget) { return 1; } }); new p(); // TypeError is thrown
The following code improperly initializes the proxy. The target
in Proxy initialization must itself be a valid constructor for the new
operator.
const p = new Proxy({}, { construct: function(target, argumentsList, newTarget) { return {}; } }); new p(); // TypeError is thrown, "p" is not a constructor
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of '[[Construct]]' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
construct | 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
See also
Proxy
handler
new
operator.Reflect.construct()