JavaScript Object.defineProperty() Method Example

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The static method Object.defineProperty() defines a new property directly on an object, or modifies an existing property on an object, and returns the object.

Example 1 - Creating a property

var user = { firstName : 'Ramesh', lastName : 'Fadatare', emailId : 'ramesh@gmail.com', age : 29 }; function test(){ Object.defineProperty(user, 'fullName', { value: user.firstName + " " + user.lastName }); console.log(user.fullName); } test();

Output:

Ramesh Fadatare

For the best learning experience, I highly recommended that you open a console (which, in Chrome and Firefox, can be done by pressing Ctrl+Shift+I), navigate to the "console" tab, copy-and-paste each JavaScript code example from this guide, and run it by pressing the Enter/Return key.

You can refer below screenshot for your testing:

Example 2 - Modifying a property

var o = {}; // Creates a new object Object.defineProperty(o, 'a', { value: 37, writable: false }); console.log(o.a); // logs 37 o.a = 25; // No error thrown // (it would throw in strict mode, // even if the value had been the same) console.log(o.a); // logs 37. The assignment didn't work. // strict mode (function() { 'use strict'; var o = {}; Object.defineProperty(o, 'b', { value: 2, writable: false }); o.b = 3; // throws TypeError: "b" is read-only return o.b; // returns 2 without the line above }());