The Proxy()
constructor is used to create Proxy
objects.
Syntax
new Proxy(target, handler)
Parameters
target
- A target object to wrap with
Proxy
. It can be any sort of object, including a native array, a function, or even another proxy. handler
- An object whose properties are functions that define the behavior of the proxy when an operation is performed on it.
Description
Use the Proxy()
constructor to create a new Proxy
object. This constructor takes two mandatory arguments:
target
is the object for which you want to create the proxyhandler
is the object that defines the custom behavior of the proxy.
An empty handler will create a proxy that behaves, in almost all respects, exactly like the target. By defining any of a set group of functions on the handler
object, you can customise specific aspects of the proxy's behavior. For example, by defining get()
you can provide a customised version of the target's property accessor.
Handler functions
This section lists all the handler functions you can define. Handler functions are sometimes called traps, because they trap calls to the underlying target object.
handler.apply()
- A trap for a function call.
handler.construct()
- A trap for the
new
operator. handler.defineProperty()
- A trap for
Object.defineProperty
. handler.deleteProperty()
- A trap for the
delete
operator. handler.get()
- A trap for getting property values.
handler.getOwnPropertyDescriptor()
- A trap for
Object.getOwnPropertyDescriptor
. handler.getPrototypeOf()
- A trap for
Object.getPrototypeOf
. handler.has()
- A trap for the
in
operator. handler.isExtensible()
- A trap for
Object.isExtensible
. handler.ownKeys()
- A trap for
Object.getOwnPropertyNames
andObject.getOwnPropertySymbols
. handler.preventExtensions()
- A trap for
Object.preventExtensions
. handler.set()
- A trap for setting property values.
handler.setPrototypeOf()
- A trap for
Object.setPrototypeOf
.
Examples
Selectively proxy property accessors
In this example the target has two properties, notProxied
and proxied
. We define a handler that returns a different value for proxied
, and lets any other accesses through to the target.
const target = { notProxied: "original value", proxied: "original value" }; const handler = { get: function(target, prop, receiver) { if (prop === "proxied") { return "replaced value"; } return Reflect.get(...arguments); } }; const proxy = new Proxy(target, handler); console.log(proxy.notProxied); // "original value" console.log(proxy.proxied); // "replaced value"
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Proxy constructor' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Proxy() constructor | 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