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

I often use the simplest way:

var variable;
if (variable === undefined){
    console.log('Variable is undefined');
} else {
    console.log('Variable is defined');
}

EDIT:

Without initializing the variable, exception will be thrown "Uncaught ReferenceError: variable is not defined..."