Is there any way to validate JSON before decode?

Use try.. catch...

import com.adobe.serialization.json.JSONParseError;try{var jsonArray:Array = JSON.decode(loader.data);}catch ( e:JSONParseError ){    //do something    trace(e);}finally{}

This solution uses as3corelib (http://as3corelib.googlecode.com/), if you use JSON.parse() please check the answer from JayC

Actionscript suppports try/catch. According to http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/JSON.html, parse throws a TypeError on failure. So it looks like something like

try{    var jsonArray:Array = JSON.parse(loader.data);}catch ( e:TypeError ){    //do something}catch (e: SomethingOtherError)  //not being literal here, just showing //you can catch more than one type of exception{}finally{    //finally always works, even if the exception is not caught above}

(edited)

The above code shouldn't need your import com.adobe.serialization.json.JSON;

The JSONParseError Thorsten mentions seems to be from the mixpanel library as3corelib library https://github.com/mikechambers/as3corelib/ which uses the JSONDecoder to deserialize https://github.com/mikechambers/as3corelib/blob/master/src/com/adobe/serialization/json/JSONDecoder.as

HOWEVER, if you want to still use the as3corelib library for some reason, to make Thorsten's code work, all you need (IIRC) would be to import com.adobe.serialization.json.JSONParseError;.