JavaScript handler.setPrototypeOf() method in JavaScript is a trap for Object.setPrototypeOf() method and it returns a Boolean value.
Syntax:
const p = new Proxy(target, {
setPrototypeOf: function(target, prototype) {
}
});
Parameters: This method accepts two parameters as mentioned above and described below:
- target: This parameter is the target object.
- prototype: This parameter is the object’s new prototype or null.
Return value: This method returns a boolean value. It returns true if the [[Prototype]] was successfully changed.
Below examples illustrate the handler.setPrototypeOf() method in JavaScript:
Example 1: In this example, we will see the use of the handler.setPrototypeOf() method in JavaScript.
javascript
const handler1 = { setPrototypeOf(gfg, gfgProto) { gfg.geneticallyModified = true; return false; }};const gfgProto = {};const gfg = { geneticallyModified: false};const proxy1 = new Proxy(gfg, handler1);console.log(Reflect.setPrototypeOf(proxy1, gfgProto));console.log(gfg.geneticallyModified);let soo = { foo: 1}let proxy = new Proxy(soo, { setPrototypeOf(target, newProto) { }});console.log('a' in proxy); |
Output:
false true false
Example 2: In this example, we will see the use of the handler.setPrototypeOf() method in JavaScript. It throws a custom error.
javascript
const handlerThrows = { setPrototypeOf(target, newProto) { throw new Error('custom error'); }};const newProto = {}, target = {};const p2 = new Proxy(target, handlerThrows);console.log(Object.setPrototypeOf(p2, newProto));console.log(Reflect.setPrototypeOf(p2, newProto)); |
Output:
Error: custom error
Supported Browsers: The browsers supported by handler.setPrototypeOf() method are listed below:
- Google Chrome 49 and above
- Edge 12 and above
- Firefox 49 and above
- Opera 36 and above
- Safari 10 and above
We have a complete list of Javascript Proxy/handler methods, to check those go through the Javascript Proxy/handler Reference article.
