Proxy.handler.construct

The handler.construct() method is a trap for the new operator.

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.

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

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

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of '[[Construct]]' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of '[[Construct]]' in that specification.	Draft

Browser compatibility

See also

• Proxy
• handler
• new operator.
• Reflect.construct()