JavaScript handler.set() Method

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

Syntax:

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.

The 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.

javascript

<script>
    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;

    console.log(proxy1.users);
</script>

Output:

"GEEKSFORGEEKS : Computer Science Portal"
"Millions"

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

javascript

<script>
    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);
    console.log(p.a);

    var x = { foo: 1 };
    var proxy = new Proxy(x, {
      set: function(target, name, value, proxy) {
    target[name] = value+" --> "+ value.toUpperCase();
      }
    });
    proxy.foo = 'geeksforgeeks';
    console.log(x.foo);
</script>

Output:

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

We have a complete list of Javascript Functions, to check those go through the Javascript Functions Complete Reference article.

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