JavaScript handler.defineProperty() Method

The handler.defineProperty() method can define the new properties. It can also modify the existing properties directly on an object. It is trap for Object.defineProper(). This method can be used in two situations.

When we wanted to ensure cross-browser support of getters and setters.
Whenever we want to define a custom property accessor.

Syntax

Parameters

Target: The target object.

Property: Retrieved property description.

Descriptor: The property being defined or modified.

Return value

This method returns a Boolean

Browser Support

Chrome	49
Edge	12
Firefox	18
Opera	36

Example 1

var target = {}
target.foo = 'bar'
document.writeln(Object.getOwnPropertyDescriptor(target, 'foo'))

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Output:

[object Object]

Example 2

var xyz = {};
var proxy = new Proxy(xyz, {
  defineProperty: function(target, name, propertyDescriptor) {
document.writeln('in defineProperty');
return Object.defineProperty(target, name, propertyDescriptor);
  }
});
Object.defineProperty(proxy, 'bar', {} );

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Output:

in defineProperty

Example 3

var xyz ={};
var hu = {};
var proxy = new Proxy(xyz, {
   defineProperty: function(target, name, propertyDescriptor) {
    document.writeln('Learn Java Script');

       return Object.defineProperty(target, name, propertyDescriptor);
  }
      });
var pro= new Proxy(hu, {
  defineProperty: function(target, name, propertyDescriptor) {
    document.writeln('Proxt Method ');
       return Object.defineProperty(target, name, propertyDescriptor);
}
      });
   Object.defineProperty(proxy, 'bar', {} );
   Object.defineProperty(pro, 'hug', {} );

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Output: