JavaScript: The Definitive Guide, 6th Edition

Name

Object.preventExtensions() — don’t allow new properties on an object

Availability

ECMAScript 5

Synopsis

Object.preventExtensions(o)

Arguments

o

The object that is to have its extensible attribute set

Returns

The argument object o.

Description

Object.preventExtensions() sets the extensible attribute of o to false so that no new properties can be added to it. This is a permanent change: once an object has been made non-extensible, it cannot be make extensible again.

Note that Object.preventExtensions() does not affect the prototype chain, and a nonextensible object can still gain new inherited properties.

Note that this is not a method to be invoked on an object: it is a global function and you must pass an object to it.

See Also

Object.freeze(), Object.isExtensible(), Object.seal(), The extensible Attribute