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JavaScript | handler.isExtensible() Method
  • Last Updated : 27 Mar, 2020

The handler.isExtensible() method in JavaScript is a trap for Object.isExtensible() method and it returns a boolean value.

Syntax:

const p = new Proxy(target, {
  isExtensible: function(target) {
  }
});

Parameters: This method accept single parameter as mentioned above and described below:

  • target: This parameter is the target object.

Return value: This method returns a Boolean value.

Below examples illustrate the handler.isExtensible() method in JavaScript:



Example 1:




<script>
const monster1 = {
  canEvolve: true
};
  
const handler1 = {
  isExtensible(target) {
    return Reflect.isExtensible(target);
  },
  preventExtensions(target) {
    target.canEvolve = false;
    return Reflect.preventExtensions(target);
  }
};
  
const proxy1 = new Proxy(monster1, handler1);
document.writeln(Object.isExtensible(proxy1));
document.writeln("<br>");
document.writeln(monster1.canEvolve);
document.writeln("<br>");
document.writeln(Object.preventExtensions(proxy1));
document.writeln("<br>");
document.writeln(Object.isExtensible(proxy1));
document.writeln("<br>");
document.writeln(monster1.canEvolve);  
</script>

Output:

true
true
[object Object]
false
false

Example 2:




<script>
const p = new Proxy({}, {
  isExtensible: function(target) {
    console.log('isExtensible method');
    return true;
  }
});
  
console.log(Object.isExtensible(p));
  
var a = {  
  canEvolve: true  
};  
var b = {   
  isExtensible(target) {  
    return true;  
  },  
   };  
const proxy1 = new Proxy(a, b);  
console.log(Object.isExtensible(proxy1));
</script>

Output:

"isExtensible method"
true
true

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

  • Google Chrome
  • Firefox
  • Opera
  • Safari
  • Edge



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