Javascript IF statement, detecting null not working

Question

I have a null variable that is behaving weird. For some reason I can't seem to detect whether or not it is null! The var is called emailFromUrl.

   console.log(emailFromUrl); //returns null
   console.log(emailFormUrl.toString()); //returns null
   console.log(emailFromUrl === null); //false!
   console.log(emailFromUrl != null); //true!
   console.log(typeof emailFromUrl); //string
   console.log(!emailFromUrl); //false!
   console.log(emailFromUrl === ""); //false

What the heck is going on here?

The answer:

   console.log(emailFromUrl === 'null'); //true!

The unfiltered console log:

Test71 | emailFromUrl : null | emailFromUrl === null : false | emailFromUrl != null : true | emailFromUrl.toString() : null | typeof emailFromUrl : string | !emailFromUrl : false | emailFromUrl === "" : false | emailFromUrl === "null" : true

What happens if you run this console.log(typeof emailFromUrl); ? — Ben Everard
– Ben Everard, Commented Jun 8, 2012 at 15:51
What kind of null are you talking about? Do you mean you've defined it but it's undefined? var emailFromUrl or that it's defined as null var emailFromUrl = '' — PitaJ
– PitaJ, Commented Jun 8, 2012 at 15:52
As far as I can tell, console.log(...) returns undefined. Your string is probably empty. Nothing prints out, it's not null, it is not null, and it has a type of string. Sounds like an empty string. — Ethan Reesor
– Ethan Reesor, Commented Jun 8, 2012 at 15:54
@PitaJ. I got the feeling, if all the lines are right, he's getting "null" instead of null. — gdoron
– gdoron, Commented Jun 8, 2012 at 16:04

raina77ow · Accepted Answer · 2012-06-08 16:02:15Z

6

Perhaps emailFromurl value is just a literal null string? ) That will explain all the results you get in your question, I think.

answered Jun 8, 2012 at 16:02

raina77ow

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raina77ow Over a year ago

It's easy actually: if emailFromUrl is truthy value (and it is, as its negation is false) and it's a string, there's only one value which will give 'null' when stringified - yep, 'null' itself. )

Charles · Accepted Answer · 2012-06-08 15:58:48Z

1

well the === operator checks the value and type. emailFromUrl is of type string not null which it why it evaluates to false there.

answered Jun 8, 2012 at 15:58

Charles

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Charles Over a year ago

Oh also, do a check to see if it is undefined, i.e. emailFromUrl == undefined

Scorpion-Prince · Accepted Answer · 2012-06-08 15:53:21Z

0

Unless you want specific logic based on it being null, you can check if the object is "falsy" (if the object is undefined, 0 or null)

if(!emailFromUrl) {
    // handle the null scenario
}

answered Jun 8, 2012 at 15:53

Scorpion-Prince

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