javascript - How to determine if variable is 'undefined' or 'null'?

How do I determine if variable is undefined or null? My code is as follows:

var EmpName = $("div#esd-names div#name").attr('class');
if(EmpName == 'undefined'){
  //DO SOMETHING

};

But if I do this, the JavaScript interpreter halts execution.

Answer

You can use the qualities of the abstract equality operator to do this:

if (variable == null){
    // your code here.
}

Because null == undefined is true, the above code will catch both null and undefined.