Checking for Undefined in Javascript

Question

I was following the below logic to check if a variable is undefined or not:

 if (variable==undefined){
////implementation
}

But found that for some cases it did not function as expected. So, tried this approach,

if(typeof(variable) == "undefined"){
/////implementation
}

So which one is most reliable?

Answer 1

Your second way is the most reliable but you don't need the parenthesis for the typeof operator. See this question.

Answer 2

if (variableName){
////implementation
}

this way is more use full than second option