The Object isExtensible() method

By Flavio Copes

Learn how the JavaScript Object.isExtensible() method checks if you can add properties to an object, returning false after freeze, seal, or preventExtensions.

This method checks if we can add new properties to an object.

Any object is extensible, unless it’s been used as an argument to

• Object.freeze()
• Object.seal()
• Object.preventExtensions()

Usage:

const dog = {}
Object.isExtensible(dog) //true

const cat = {}
Object.freeze(cat)
Object.isExtensible(cat) //false

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