AJAX: Check if a string is JSON?

Question

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 1

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.

Answer 2

Hers's the jQuery alternative...

try {   var jsonObject = jQuery.parseJSON(yourJsonString); } catch(e) {   // handle error  }