By: Comfortably Anonymous
Times Read: 2,313
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Topic: Programming: jQuery/Javascript
Sending a null value in JSON is really easy, but it seems like every time you go to look up how to actually represent a null value in a JSON call to an AJAX web service you instead end up with a bunch of discussion on using JSON.parse / JSON.stringify and helper methods to do just that. [No slam on using the JSON object, it's extremely helpful, just some times you don't need it.]
But sometimes you just need to know "How do I represent a NULL value?" or "Why does the web service keep choking on my null values?"
It's more of a mental adjustment than anything super tricky.
Typically when you run into this issue, you've been attempting to build your JSON string using variables. Something like:
var x = 22;
var y = null;
var json = "{"; // Open bracket
json += "'valX':'" + x + "',"; // Set value of X
json += "'valY':'" + y + "'"; // Set value of Y
json += "}"; // Close bracket
Which gives you a resulting JSON string of:
{'valX':'22','valY':'null'}
This will cause your web service to choke on the the value assigned to valY. Why? Because you are passing the null value as a string. (See the 'null' there? Yep, it's got single quotes around it. That's the problem.)
To pass a null value is easy, just don't put it in quotes!! Easy as that, same thing only no quotes around null values:
{'valX':'22','valY':null}
Your web service will now happily accept your new value. :)
While there's probably better ways to handle nulls, I just use an easy brute-force approach with a NullCheck() function:
function NullCheck(value)
{
if (value == null)
return "null";
else
return "'" + value + "'"; // Wrap non-null values in single quotes
}
I use it inline when building my JSON string: (Above example modified to use NullCheck())
var x = 22;
var y = null;
var json = "{"; // Open bracket
json += "'valX':" + NullCheck(x) + ","; // Set value of X
json += "'valY':" + NullCheck(y) ; // Set value of Y
json += "}"; // Close bracket
Which outputs:
{'valX':'22','valY':null}
Hope this helps, enjoy!