JavaScript Object.preventExtensions()
Example
// Create Object
const person = {firstName:"John", lastName:"Doe"};
// Prevent Extensions
Object.preventExtensions(person);
// This will throw an error
person.nationality = "English";
Try it Yourself »
const person = {firstName:"John", lastName:"Doe"};
// Prevent Extensions
Object.preventExtensions(person);
// This will throw an error
person.nationality = "English";
More Examples Below !
Description
The Object.preventExtensions() method prevents adding properties to an object.
You can use Object.isExtensible() to check if an object is extensible.
Related Methods:
Object.preventExtensions() allows modifications, but prevents addition of properties.
Object.seal() allows modifications, but prevents additions and deletions of properties.
Object.freeze() prevents modifications, additions and deletions of properties.
Object.isExtensible() returns true if an object is extensible.
Object.isSealed() returns true if an object is sealed.
Object.isFrozen() returns true if an object is frozen.
Syntax
Object.preventExtensions(object)
Parameters
Parameter
Description
object
Required.
The object to prevent extensions to.
The object to prevent extensions to.
Return Value
Type
Description
Object The object that was modified.
More Examples
Example
// Create Array
const fruits = ["Banana", "Orange", "Apple", "Mango"];
Object.preventExtensions(fruits);
// This will throw an error:
fruits.push("Kiwi");
Try it Yourself »
const fruits = ["Banana", "Orange", "Apple", "Mango"];
Object.preventExtensions(fruits);
// This will throw an error:
fruits.push("Kiwi");
Browser Support
Object.preventExtensions() is an ECMAScript5 (ES5 2009) feature.
JavaScript 2009 is supported in all browsers since July 2013:
| Chrome 23 |
IE/Edge 11 |
Firefox 21 |
Safari 6 |
Opera 15 |
| Sep 2012 | Sep 2012 | Apr 2013 | Jul 2012 | Jul 2013 |