Proxy() constructor
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 customize specific aspects of the proxy's behavior. For example, by
defining get()
you can provide a customized 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 Language Specification # sec-proxy-constructor |
Browser compatibility
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