Widely availableSupported across all major browsers. Safe to use in production.
Language core Widely available

Proxy and Reflect

The Proxy and Reflect JavaScript built-ins intercept and define custom behavior for fundamental language operations (such as property lookup, assignment, enumeration, or function invocation).

Language core

Overview

The Proxy and Reflect JavaScript built-ins intercept and define custom behavior for fundamental language operations (such as property lookup, assignment, enumeration, or function invocation).

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
Proxy
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Proxy.Proxy

The Proxy() constructor creates Proxy objects.
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Proxy.handler.apply

The handler.apply() method is a trap for the [[Call]] object internal method, which is used by operations such as function calls.
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Proxy.handler.construct

The handler.construct() method is a trap for the [[Construct]] object internal method, which is used by operations such as the Operators/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 be a valid constructor.
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Proxy.handler.defineProperty

The handler.defineProperty() method is a trap for the [[DefineOwnProperty]] object internal method, which is used by operations such as Object.defineProperty().
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Proxy.handler.deleteProperty

The handler.deleteProperty() method is a trap for the [[Delete]] object internal method, which is used by operations such as the Operators/delete operator.
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Proxy.handler.get

The handler.get() method is a trap for the [[Get]] object internal method, which is used by operations such as property accessors.
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Proxy.handler.getOwnPropertyDescriptor

The handler.getOwnPropertyDescriptor() method is a trap for the [[GetOwnProperty]] object internal method, which is used by operations such as Object.getOwnPropertyDescriptor().
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Proxy.handler.getPrototypeOf

The handler.getPrototypeOf() method is a trap for the [[GetPrototypeOf]] object internal method, which is used by operations such as Object.getPrototypeOf().
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Proxy.handler.has

The handler.has() method is a trap for the [[HasProperty]] object internal method, which is used by operations such as the Operators/in operator.
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Proxy.handler.isExtensible

The handler.isExtensible() method is a trap for the [[IsExtensible]] object internal method, which is used by operations such as Object.isExtensible().
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Proxy.handler.ownKeys

The handler.ownKeys() method is a trap for the [[OwnPropertyKeys]] object internal method, which is used by operations such as Object.keys(), Reflect.ownKeys(), etc.
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Proxy.handler.preventExtensions

The handler.preventExtensions() method is a trap for the [[PreventExtensions]] object internal method, which is used by operations such as Object.preventExtensions().
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Proxy.handler.set

The handler.set() method is a trap for the [[Set]] object internal method, which is used by operations such as using property accessors to set a property's value.
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Proxy.handler.setPrototypeOf

The handler.setPrototypeOf() method is a trap for the [[SetPrototypeOf]] object internal method, which is used by operations such as Object.setPrototypeOf().
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Proxy.revocable

The Proxy.revocable() static method creates a revocable Proxy object.
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Other
javascript.builtins.Reflect

The Reflect namespace object contains static methods for invoking interceptable JavaScript object internal methods. The methods are the same as those of proxy handlers.
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Built-in object
Reflect.apply

The Reflect.apply() static method calls a target function with arguments as specified.
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Reflect.construct

The Reflect.construct() static method is like the Operators/new operator, but as a function. It is equivalent to calling new target(...args). It additionally allows to specify a different new.target value.
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Reflect.defineProperty

The Reflect.defineProperty() static method is like Object.defineProperty() but returns a Boolean.
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Reflect.deleteProperty

The Reflect.deleteProperty() static method is like the Operators/delete operator, but as a function. It deletes a property from an object.
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Reflect.get

The Reflect.get() static method is like the property accessor syntax, but as a function.
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Reflect.getOwnPropertyDescriptor

The Reflect.getOwnPropertyDescriptor() static method is like Object.getOwnPropertyDescriptor(). It returns a property descriptor of the given property if it exists on the object, undefined otherwise.
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Reflect.getPrototypeOf

The Reflect.getPrototypeOf() static method is like Object.getPrototypeOf(). It returns the prototype of the specified object.
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Reflect.has

The Reflect.has() static method is like the in operator, but as a function.
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Reflect.isExtensible

The Reflect.isExtensible() static method is like Object.isExtensible(). It determines if an object is extensible (whether it can have new properties added to it).
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Reflect.ownKeys

The Reflect.ownKeys() static method returns an array of the target object's own property keys.
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Reflect.preventExtensions

The Reflect.preventExtensions() static method is like Object.preventExtensions(). It prevents new properties from ever being added to an object (i.e., prevents future extensions to the object).
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Reflect.set

The Reflect.set() static method is like the property accessor and assignment syntax, but as a function.
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Reflect.setPrototypeOf

The Reflect.setPrototypeOf() static method is like Object.setPrototypeOf() but returns a Boolean. It sets the prototype (i.e., the internal [[Prototype]] property) of a specified object.
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1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)
Notes 1 item(s)
Implementation note
  • In Firefox 42, the implementation got updated to reflect the final ES2015 specification: The result is now checked if it is an array and if the array elements are either of type string or of type symbol. Enumerating duplicate own property names is not a failure anymore.

Syntax

JAVASCRIPT 
const handler = {
  get(target, prop) {
    return prop in target ? target[prop] : `${prop} is undefined`;
  },
  set(target, prop, value) {
    if (typeof value !== 'number') throw TypeError('Only numbers allowed');
    target[prop] = value;
    return true;
  }
};

const obj = new Proxy({}, handler);
obj.x = 42;    // OK
obj.missing;   // 'missing is undefined'

Live demo

Proxy Basics

Object. operation inta-sept.get / set trap definition. with Proxy

PreviewFullscreen

valid-tion withobject

Set trap in value. Verification implementation.

PreviewFullscreen

Reflect API

Objectoperation functionization.Proxy and combinationuse. with Reflect

PreviewFullscreen

Use cases

  • Using Proxy and Reflect

    The Proxy and Reflect JavaScript built-ins intercept and define custom behavior for fundamental language operations (such as property lookup, assignment, enumeration, or function invocation).

Cautions

  • No specific concerns. Stable across all major browsers.

Accessibility

  • When updating the DOM dynamically, announce important changes to assistive technology with aria-live regions.

Related links

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