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 }; <div id="esd-names"> <div id="name"></div> </div> But if I do this, the JavaScript interpreter halts execution. Answer: You can do this: if (variable == null){ // your code here. } Check MDN for details on equality tests in JS. null == undefined is true, but null === undefinedis false. Thus the code above, as is, will catch