How to check if a variable or object is undefined?

Question

I always thought I could just check an undefined var by comparing it to undefined, but this is the error I get in the chrome console :

Answer 1

Process 1:

if (jQuery) {  
    // jQuery is loaded  
} else {
    // jQuery is not loaded
}

Process 2:

if (typeof jQuery == 'undefined') {  
    // jQuery is not loaded  
} else {
    // jQuery is loaded
}