JavaScript handler.isExtensible() Method

The handler.isExtensible() method a trap for Object.isExtensible(). We can be mostly used for logging or auditing calls to Object.isExtensible (determine if an object is "extensible").

Syntax

Parameters

target: The target object.

Return value

Return a Boolean value.

Browser Support

Chrome	Compatibility unknown
Edge	Compatibility unknown
Firefox	31
Opera	Compatibility unknown

Example 1

var x = { foo: 1 };
var proxy = new Proxy(x, {
  isExtensible: function(target) {
    document.writeln('in isExtensible');
    //expected output: in isExtensible 
 return Object.isExtensible(target);
  }
});
document.writeln(Object.isExtensible(proxy));
//expected output: true 
document.writeln("<br/>")
Object.preventExtensions(proxy);
document.writeln(Object.isExtensible(proxy));

//expected output: false

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Output:

in isExtensible true 
in isExtensible false

Example 2

const pro={
too:1 }
const  proxy = new Proxy(pro, {
  isExtensible: function(target) {
    document.writeln(' in value : ');
    return true;
  }
});

document.writeln(Object.isExtensible(proxy));
//expected output: in value : true

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Output:

in value : true

Example 3

var a = {
  canEvolve: true
};
var b = { 
  isExtensible(target) {
    return true;
  },
   };
const proxy1 = new Proxy(a, b);
document.writeln(Object.isExtensible(proxy1));
// expected output: true

Test it Now

Output: