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).

Syntax

var 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:

Invariants

If the following invariants are violated, the proxy will throw a TypeError:

  • The result must be an Object.

Examples

The following code traps the new operator.

var 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.

var 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.

var p = new Proxy({}, {
  construct: function(target, argumentsList, newTarget) {
    return {};
  }
});

new p(); // TypeError is thrown, "p" is not a constructor

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of '[[Construct]]' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of '[[Construct]]' in that specification.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support491218 No3610
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support4949 Yes18 No3610

See also

Document Tags and Contributors

 Contributors to this page: fscholz, Piterden, chrahunt, nmve, kdex, fasttime, arai
 Last updated by: fscholz,