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Showing content from https://webplatform.github.io/docs/javascript/Object/isExtensible below:

isExtensible · WebPlatform Docs

isExtensible Summary

Returns a value that indicates whether new properties can be added to an object.

Syntax

Object.isExtensible( object )

object: Required. The object to test.

Return Value

true if the object is extensible, which indicates that new properties can be added to the object; otherwise, false.

Examples

The following example illustrates the use of the Object.isExtensible function.


 var obj = { pasta: "spaghetti", length: 10 };

 
 Object.preventExtensions(obj);

 
 obj.newProp = 50;
 document.write(obj.newProp);

 
 undefined

Remarks

For information about how to set property attributes, see Object.defineProperty Function. To obtain the attributes of a property, you can use the Object.getOwnPropertyDescriptor Function.

The following related functions prevent the modification of object attributes.

The following functions return true if all of the conditions marked in the following table are true.

Function Object is extensible? configurable is false for all properties? writable is false for all data properties? Object.isExtensible Yes No No Object.isSealed No Yes No Object.isFrozen No Yes Yes Exceptions

If the object argument is not an object, a TypeError exception is thrown.