How do I check for null values in JavaScript?

javascript null compare comparison
Mahdi_Nine picture Mahdi_Nine · May 14, 2011 · Viewed 1.3M times · Source

How can I check for null values in JavaScript? I wrote the code below but it didn't work.

if (pass == null || cpass == null || email == null || cemail == null || user == null) {      

    alert("fill all columns");
    return false;  

}

And how can I find errors in my JavaScript programs?

Answer

Mark Kahn picture Mark Kahn · May 14, 2011

Javascript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:

if(!pass || !cpass || !email || !cemail || !user){

Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN

Please note that if you are specifically checking for numbers it is a common mistake to miss 0 with this method, and num !== 0 is preferred (or num !== -1 or ~num (hacky code that also checks against -1)) for functions that return -1, e.g. indexOf)

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