JavaScript .isExtensible()

The .isExtensible() is a static method that returns true if the given object can have properties added to it and false if the object cannot have properties added to it.

Syntax

Object.isExtensible(newObject);

• newObject: It is the object to be checked whether it is extensible.

Note: Objects are extensible by default. An object can be made non-extensible by using Object.freeze(), Object.preventExtensions, or Object.seal(). A non-extensible object can still have its properties modified.

Example

The following code will check if an object is extensible or not using the .isExtensible() method:

const characters = {
  ArthurDent: 'Earth',
  FordPrefect: 'Betelgeuse Five',
  ZaphodBeeblebrox: 'Betelgeuse Seven',
};

console.log(Object.isExtensible(characters));
Object.preventExtensions(characters);
console.log(Object.isExtensible(characters));

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The output for the above will be:

true
false

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Codebyte Example

Following is a runnable example that demonstrates the Object.isExtensible() static method:

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