The undefined property indicates that a variable has not been assigned a value, or not declared at all. The type of undefined value is undefined too.
var user; // Value is undefined, type is undefined
Any variable can be emptied by setting the value to undefined.
user = undefined
If you like this question & answer and want to contribute, then write your question & answer and email to freewebmentor[@]gmail.com. Your question and answer will appear on FreeWebMentor.com and help other developers.