AJAX: Check if a string is JSON?

javascript ajax json validation

Nick Heiner · Feb 22, 2010 · Viewed 92.6k times · Source

My JavaScript sometimes crashes on this line:

var json = eval('(' + this.responseText + ')');

Crashes are caused when the argument of eval() is not JSON. Is there any way to check if the string is JSON before making this call?

I don't want to use a framework - is there any way to make this work using just eval()? (There's a good reason, I promise.)

Answer

If you include the JSON parser from json.org, you can use its parse() function and just wrap it in a try/catch, like so:

try
{
   var json = JSON.parse(this.responseText);
}
catch(e)
{
   alert('invalid json');
}

Something like that would probably do what you want.