How to check if a variable is not null?

Question

I know that below are the two ways in JavaScript to check whether a variable is not null, but I’m confused which is the best practice to use.

Should I d

Answer 1

Sometimes if it was not even defined is better to be prepared. For this I used typeof

if(typeof(variable) !== "undefined") {
    //it exist
    if(variable !== null) {
        //and is not null
    }
    else {
        //but is null
    }
}
else {
    //it doesn't
}