The Object isExtensible() method

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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