How to know if a variable is null

peace2007 · September 29th, 2007, 03:46 PM

Hi,

I try to check if a variable is null via following code but I don't get an expected result:

Code:

 var askedUser = re.responseText;
            askedUser = askedUser.substr(0, askedUser.indexOf('&',0));
            if(askedUser != null  && askedUser != " ")
            {    do something}

the if() returns true whether askedUser == "" or askedUser = "a value"!
Could anyone guide me please?

dparsons · September 29th, 2007, 04:23 PM

My previous statement was inaccurate, sorry about that, it has been a long day. What happens if you phsyically set the value?

var askedUser = 'Some Value'

Do you drop into the if or no?

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joefawcett · September 29th, 2007, 06:31 PM

It's not clear whether peace2007 wants to test for an empty string or a single space. Perhaps the test should be:

Code:

if (askedUser)
{
  //this will run if user is not null and not an empty string.
}

--

Joe (Microsoft MVP - XML)

peace2007 · September 30th, 2007, 12:57 AM

I'm checking for an empty string; either I physically set the value or modify the condition as "if (askedUser)" I don't get the desired result!
The whole process is as follows:
I get a value from server, then remove the extra characters from the end of it, and then I check if the value is an empty string (I set the return result of server to string.empty by default)
While I'm tracing my code when I reach to the statement before if condition, the value of askedUser is (askedUser = "") but the if() returns true!

Thanks for your replies

joefawcett · September 30th, 2007, 07:02 AM

Show your exact code again, last time it checked for a string of one space, not an empty one.

--

Joe (Microsoft MVP - XML)

peace2007 · September 30th, 2007, 07:12 AM

Here is the exact copy of my code:

Code:

url = 'Server.aspx?action=GetVideoReq&session=' + rnd ;
    var re = getAjax();

    re.onreadystatechange = function(){    
        if( re.readyState == 4 && re.status == 200 ) 
        {    
            var askedUser = re.responseText;
            askedUser = askedUser.substr(0, askedUser.indexOf('&',0));  
            if(askedUser != null  && askedUser != "")
            {    
                ...}

In which when askedUser == "" the if() returns true. I put nothing between two quotation marks.

joefawcett · September 30th, 2007, 07:18 AM

Okay, can you add

Code:

alert("!" + askedUser + "!");

just before the "if" line?

--

Joe (Microsoft MVP - XML)

peace2007 · September 30th, 2007, 07:28 AM

I did, it seems it includes spaces, the alert box displays:

Code:

!

!

joefawcett · September 30th, 2007, 07:50 AM

So you've got some newline characters in there. Looks like you might have to trim the data before testing or find out why your web service is sending back that combination.

--

Joe (Microsoft MVP - XML)

peace2007 · September 30th, 2007, 10:08 AM

Thank you Joe!
This is the second time you're resolving my problem, I really appreciate that