Proxy() constructor - JavaScript | MDN
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Proxy() constructor
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
Learn more
See full compatibility
The Proxy() constructor creates Proxy objects.
In this article
Syntax
Description
Examples
Specifications
Browser compatibility
See also
Syntax
js
new Proxy(target, handler)
Note:
Proxy() can only be constructed with new. Attempting to call it without new throws a TypeError.
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 proxy
handler 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 and
Object.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.
js
const target = {
notProxied: "original value",
proxied: "original value",
};
const handler = {
get(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® 2027 Language Specification
# sec-proxy-constructor
Browser compatibility
Enable JavaScript to view this browser compatibility table.
See also
Meta programming guide
Reflect
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This page was last modified on May 22, 2026 by MDN contributors.
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