Check 'undefined' in JavaScript

To check 'undefined' in JavaScript,

you can do the following:

console.log(typeof a === "undefined")
true

You can print the type of an 'undefined' variable as follows:

console.log(typeof a);
undefined

and you can print the type of the 'undefined' itself as follows:

console.log(typeof (typeof a));
string

Reference:
http://stackoverflow.com/questions/3390396/how-to-check-for-undefined-in-javascript