How to check a not-defined variable in JavaScript

Question

I wanted to check whether the variable is defined or not. For example, the following throws a not-defined error

alert( x );

How can I cat

Answer 1

An even easier and more shorthand version would be:

if (!x) {
   //Undefined
}

OR

if (typeof x !== "undefined") {
    //Do something since x is defined.
}