How can I determine if a variable is 'undefined' or 'null'?

Question

How do I determine if variable is undefined or null?

My code is as follows:

var EmpN         


        

Answer 1

jQuery check element not null:

var dvElement = $('#dvElement');

if (dvElement.length  > 0) {
    // Do something
}
else{
    // Else do something else
}