How to check undefined, empty and null in JavaScript/JQuery ?

If you are working on jquery and However you want to check variable is undefined or not then you can easily check by typeof operator, which is simple, fast and cross-platform:

if(typeof i == "undefined"){
 alert('undefined');
}

If you are working on jquery and However you want to check variable is empty or not then you can easily check by compare with empty string:

if(i == ''){
 alert('Empty');
}

If you are working on jquery and However you want to check variable is null or not then you can easily check by compare with "null":

if(i == null || i == NULL){
 alert('null');
}

Try this......