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JavaScript Handler set() Method

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JavaScript handler.set() method in JavaScript is a trap for setting a property value. This method returns a boolean value.


const p = new Proxy(target, {
      set: function(target, property, value, receiver) {

Parameters: This method accepts four parameters as mentioned above and described below: 

  • target: This parameter holds the target object.
  • property: This parameter holds the name or Symbol of the property.
  • value: This parameter holds the new value of the property.
  • receiver: This parameter holds the object to which the assignment was originally directed.

Return value: This method always returns a boolean value.

Below examples illustrate the handler.set() Method in JavaScript:

Example 1: In this example, we will see the basic use of the handler.set() Method in JavaScript.


function gfg() {
    this.users = "Millions";
const handler1 = {
    set(obj, prop, value) {
        if ((prop === 'users') && ((value % 2) !== 0)) {
            console.log('GEEKSFORGEEKS : Computer Science Portal');
        } else {
            return Reflect.set(...arguments);
const gfg1 = new gfg();
const proxy1 = new Proxy(gfg1, handler1);
proxy1.users = 1;


"GEEKSFORGEEKS : Computer Science Portal"

Example 2: In this example, we will see the basic use of the handler.set() Method in JavaScript.


const p = new Proxy({}, {
    set: function (target, prop, value, receiver) {
        target[prop] = value;
        console.log('property set: ' + prop + ' = ' + value);
        return true;
console.log('a' in p);
p.a = 10;
console.log('a' in p);
let x = { foo: 1 };
let proxy = new Proxy(x, {
    set: function (target, name, value, proxy) {
        target[name] = value + " --> " + value.toUpperCase();
}); = 'geeksforgeeks';


"property set: a = 10"
"geeksforgeeks --> GEEKSFORGEEKS"

Supported Browsers: The browsers supported by handler.set() method are listed below. 

  • Google Chrome 49 and above
  • Edge 12 and above
  • Firefox 18 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.

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Last Updated : 22 May, 2023
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