Debugging Javascript Code

The usual technique is using alert to check variable, function return or a line broken.
But there's a more advance technique for do debug error - use try catch block.

try{

    varq;

}catch(err){

    alert(err);

}

ouput: ReferenceError: varq is not defined

type for other output are:

alert();

output:

    [Exception... "Not enough arguments 

    [nsIDOMWindowInternal.alert]"  nsresult: "0x80570001

    (NS_ERROR_XPC_NOT_ENOUGH_ARGS)"  location: "JS frame ::

    http://htmledit.squarefree.com/ :: 

    :: line 5"  data: no]

output:

    TypeError: Doc.getElementsByTagName("lang")[i] is undefined

          

                

Debugging Javascript Code