The syntax of the isExtensible()
method is:
Object.isExtensible(obj)
The isExtensible()
method, being a static method, is called using the Object
class name.
isExtensible() Parameters
The isExtensible()
method takes in:
- obj - The object which should be checked.
Return value from isExtensible()
- Returns a
Boolean
indicating whether or not the given object is extensible.
Note: An object can be marked as non-extensible using Object.preventExtensions()
, Object.seal()
, or Object.freeze()
.
Example: Using isExtensible()
// New objects are extensible.
let empty = {};
console.log(Object.isExtensible(empty)); // true
Object.preventExtensions(empty);
console.log(Object.isExtensible(empty)); // false
// Sealed objects are by definition non-extensible.
let sealed = Object.seal({});
console.log(Object.isExtensible(sealed)); // false
// Frozen objects are also by definition non-extensible.
let frozen = Object.freeze({});
console.log(Object.isExtensible(frozen)); // false
Output
true false false false
Recommended Reading: JavaScript Object.preventExtensions()