JS: Object.isExtensible

JS: Object.isExtensible

Object.isExtensible(obj)

Return true if a object obj is an object and is extensible, else false.

[see JS: What's Object?]

Extensible means properties can be added.

[see JS: Prevent Adding Property]

// check if a object is extensible

console.log( Object.isExtensible( {} )); // true
// return false for non object
console.log( Object.isExtensible( 3 )); // false

Reflect.isExtensible

If using ES2015, use Reflect.isExtensible instead. It throws error if argument is not object.

[see JS: Reflect.isExtensible]

Reference

ECMAScript® 2016 Language Specification#sec-object.isextensible

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