a developer's notes – a semi-technical web development BLOG

September 5, 2011

Check for null or undefined in Javascript

Filed under: Javascript / JQuery — Duy Nguyen @ 12:34 pm
Tags: , , , ,

Here is how you can check if a variable is null or undefined.


function MyMethod() {
     var myVar = document.getElementById('something');
     if(typeof(myVar) !== 'undefined' && myVar!= null) {
          return myVar.checked;
     }
}

OR this…

if( value ) {
}

will evaluate to true if value is not:

null
undefined
NaN
empty string (“”)
0
false

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