A handler is an object whose properties are functions that define the behaviour of the proxy when an operation is performed on it. 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 behaviour. For example, by defining get() you can provide a customized version of the target’s property accessor.
Syntax:
new Proxy(target, handler)
proxy constructor(): Used to create a proxy object which takes two parameters.
Parameters:Â
- target: 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 behaviour of the proxy when an operation is performed on it.
List of Handler Methods: This section lists all the handler methods you can define. Handler methods 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.
Example: In this example, the target has two properties, string and num. We define a handler that returns a different value for num, and lets any other accesses through to the target.
Javascript
<script>const target = {    string: "GeeksForGeeks",    num: 123};const handler = {    get: function (target, prop, receiver) {        if (prop === "string") {            return "GeeksForGeeks";        }        return Reflect.get(...arguments);    }};const obj = new Proxy(target, handler);console.log(obj.string); // "GeeksForGeeks"console.log(obj.num);   // "123"</script> |
Output:
GeeksForGeeks 123
