javascript 'if' not catching null from ajax

Question

I have a javascript ajax request that return's null if nothing is found and then displays that no results were found to the user. This was working fine before but for some reason has stopped. The IF statement no longer seems to catch the null.

//on success
        success: function(data) {

            if(data == 'null') {
                buildaccordion("<h3>No Results Found</h3><div>No Data to Show.</div>");
                return;
            }

When I look at the response from the php side of things, I am indeed being send the text 'null' from the server. I've also checked with the built in debugger in firefox and the value of data is "null". But the if statement does not catch it!?

This was working fine before and I can not see what would be causing this.

I have also tried

== null

=== null

=== 'null'

possible duplicate of how to check null values in javascript? — Pranav C Balan
– Pranav C Balan, Commented Jan 15, 2014 at 15:52
My bet is there is whitespace console.log(escape(data)); that is why using a format like JSON is better — epascarello
– epascarello, Commented Jan 15, 2014 at 15:55
When I look at the response from the php side of things, I am indeed being send the text 'null' from the server Then this observation is in error. How did you determine it? In particular, check for whitespace. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 15, 2014 at 15:56

Hanky Panky · Accepted Answer · 2014-01-15 15:59:14Z

4

Since you mentioned its type already shows as string, You can do:

if(data.trim()=='null')

Previous Answer:

When you say if data=='null' you are actually checking if data is the string null

 if(data == 'null')

Should be

 if(!data)

Or

if(typeof data === 'undefined')

edited Jan 15, 2014 at 15:59

answered Jan 15, 2014 at 15:51

Hanky Panky

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9 Comments

0xFADE Over a year ago

Oh yeah the undefined type. Nice.

Kai Qing Over a year ago

He's saying he is getting the text "null" - perhaps he should change his handler to actually return null instead of a string

Spokey Over a year ago

won't data be automatically converted into a string ?

Hanky Panky Over a year ago

Mmmm if its about a string then his solution should already work. I was confused by the title and answered based on question title rather than the different problem in the body.

user1853181 Over a year ago

I guess trim() will never catch   Cant think of other legitimate cases of returning a whitespace-like values as opposed to null right now, seems fine.

|

0xFADE · Accepted Answer · 2014-01-15 15:52:23Z

1

You can try if( !data )

null and 0's are all the same.

answered Jan 15, 2014 at 15:52

0xFADE

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Comments

user1853181 · Accepted Answer · 2014-01-15 15:58:34Z

1

In order to be sure (since you do not know precisely what the type of the return value is), better implement a catch-all solution:

if((!data) || (data == 'null') || (typeof data === 'undefined') || (!data.length)) {
    // No results
}

answered Jan 15, 2014 at 15:58

user1853181

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user1537366 · Accepted Answer · 2014-01-15 15:54:23Z

0

Is there a space somewhere? Maybe if( data.replace(/^\s+/,"").replace(/\s+$/,"")=="null" ) ... will work?

answered Jan 15, 2014 at 15:54

user1537366

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1 Comment

user1537366 Over a year ago

From what I remember, just two years or so in the past, there was no member named trim on a String object.

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