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).
handler.construct()
Try it
Syntax
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 myFunction(...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 Language Specification # sec-proxy-object-internal-methods-and-internal-slots-construct-argumentslist-newtarget |
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
construct |
49
|
12
|
18
|
No
|
36
|
10
|
49
|
49
|
18
|
36
|
10
|
5.0
|
1.0
|
6.0.0
|
See also
Proxy
handler
-
new
operator. Reflect.construct()
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/construct