How do I check for null values in JavaScript

Questions

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?

Answers

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)

Source

License : cc by-sa 3.0

http://stackoverflow.com/questions/6003884/how-do-i-check-for-null-values-in-javascript

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