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?

see the questions under the Related section on the right side of the page. — Anurag, Jun 20 '11 at 05:26
possible duplicate of [Detecting an undefined object property in JavaScript](http://stackoverflow.com/questions/27509/detecting-an-undefined-object-property-in-javascript) — Asaph, Jun 20 '11 at 05:27

score 6 · Accepted Answer · edited May 23 '17 at 11:58

6

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

edited May 23 '17 at 11:58

Community

answered Jun 20 '11 at 05:25

Asaph

amit kate · Answer 2 · 2014-09-30T12:29:35.093

3

if (variableName){
////implementation
}

this way is more use full than second option

edited Sep 30 '14 at 12:29

answered Oct 09 '12 at 13:02

amit kate

2 Answers2