Catching errors inside window.onerror?

Question

I've setup a window.onerror handler to catch errors. Its purpose? To concat a string for each time an error occurs, then another handler window.onunload sends it off to the Server. (Presumably with all the errors).

Problem is, it's only able to send the first error over, because after the onerror handler event fires for the first time, the error isn't caught and thus the script terminates...

Is there a way around this?

ErrorManager: (function () {
        function Init(message) {
            InitErrorHandler();
            InitAjaxHandler();
            setTimeout("Interface.ErrorManager.SendErrorsToAjax()", 8000);
        }
        function InitErrorHandler() {
            Data.ErrorHandlerText = "";
            Data.ErrorHandlerCount = 0;
            window.onerror = function(errorMessage, url, line) {
                if(IsInIgnoreList(errorMessage)) { return; }
                Data.ErrorHandlerText += ("Error: "+(Data.ErrorHandlerCount+1)+" <br /><br />");
                //Get error specific info
                Data.ErrorHandlerText += escape(errorMessage) + "<br />";
                Data.ErrorHandlerText +=  escape(url) + "<br />";
                Data.ErrorHandlerText +=  escape(line) + "<br />";
                Data.ErrorHandlerCount++;
                console.log("BOOM"+errorMessage);
            }
        }

        function InitAjaxHandler() {
            window.onbeforeunload = function() { //when browser closed
                Data.ErrorHandlerCount > 0 && SendErrorsToAjax();
            }
        }
        function SendErrorsToAjax() {
            PrepareErrorsForAjax();
            $.getJSON(Interface.Utility.PrefixURL('/ajax/sendfeedback/handlejserrors/'+Data.ErrorHandlerText));
        }
        function IsInIgnoreList(str) {
            return str.indexOf('nsIDOMSVGLocatable') != -1 ? true : false;
        }

        function PrepareErrorsForAjax() {
            var preText = "<br /><br />A user has encountered a few errors: <br /><br />";
            //Get session info
            var userAgent, activePageID, accountNO, consumerNO;
            userAgent = escape(navigator.userAgent);
            preText += "User agent: "+userAgent+" <br />";

            if($.mobile.activePage) {
                activePageID = $.mobile.activePage.attr('id');
                preText += "Page ID: "+activePageID+" <br />";
            }
            //Get info that may or may not be set
            console.log("AUTH JSON "+Data.authJSON);
            console.log("CONSUMER JSON "+Data.authJSON.consumers);
            if(Data.authJSON && localStorage.lastConsumerNo) {
                preText += "Account Number: " +Data.authJSON.accountId+" <br />";
                preText += "Consumer Number: "+ localStorage.lastConsumerNo+" <br />";
            }
            preText += "<br /> The following errors were encountered:<br /><br />";
            Data.ErrorHandlerText = preText + Data.ErrorHandlerText;
        }
        return {
            Init: Init,
            SendErrorsToAjax: SendErrorsToAjax
        }
    })(),

Answer 1

Add it in a seperate <script> tag, so that window.onerror is not bothered by script errors in other script tags.

DEMO

<script>
    var trackErrorMsg = '';
    window.onerror = function(msg, url, lineNo)  {
      trackErrorMsg += msg;     
    }
</script>

Please Note the above doesn't stop error being logged in the browser console.. The above code is just to track the errors.. You should use try...catch to handle errors in any specific sections.

DEMO - To show that it doesn't work when you have it on the same execution context.