Legacy Javascript from a SPA written in 2007

Model.js

//Vintage Jquery 1.3
$.post("DataFiles/Registration.ashx",
{
    //Actual values sent to the server are formatted are broken into 3 segments, separated by a tilde
    //The first is the type to which the value should be cast at the server, the second the actual value
    //The third segment, "fin" specifies the server should not validate or update those fields
    //We have the best code. Tremendous code, people tell me all the time.
    new_ncoqfrname: $("#txtRegNo").attr("type") + "~" + $("#txtRegNo").val() + "~fin",
    new_federalidfein: $("#new_federalidfein").attr("type") + "~" + $("#new_federalidfein").val() + "~fin",
    new_ncoqfrfinancialperiodstartdate: "datetime" + "~" + $("#new_ncoqfrfinancialperiodstartdate").val() + "~fin",
    new_ncoqfrfinancialperiodenddate: "datetime" + "~" + $("#new_ncoqfrfinancialperiodenddate").val() + "~fin",
    /* Not pictured: an additional hundred lines of this */
    
    //Apparently, at some point the client wanted a snapshot of what the customer sees when filling out the form.
    //Why not send the entire HTML file to the server via AJAX?
    htmldocument: "HTMLdoc" + "~" + getHTML()
}, function(msg) {
    //We can redirect the user to an arbitrary URL fragment supplied after the tilde
    if (msg.toString().match("success~")) {
        $('#btnSubmit').attr("disabled", true);
        if (msg.toString().match("pgnotsetto1")) {
            //This will be super helpful to our end users
            alert('Payment Gateway Option in webconfig is not set to 1.');
            location.href = "edit.aspx";
        }
        else if (msg.toString().match("nofeepaid")) {
            alert('The application was submitted. There will be no fee paid with this transaction.  You will receive email confirmation within one day.  Thank you.');
            location.href = "edit.aspx";
        }
        else {
            var ReturnString;
            ReturnString = msg.toString().split('~');
            location.href = ReturnString[1];
        }
    }
    else if (msg == "Timeout") {
        alert("Sorry, your connection to the server has timed out");
        location.href = "login.aspx";
    }
    else if (msg != "Saved") {
        alert('Error saving data , ' + msg + " Taking you back to Main page.");
        location.href = "edit.aspx";
    }
    else {
        //I don't know.
        if (document.getElementById("AppType").value == "New")
            location.href = "Change.aspx";
        else
            location.href = "FinancialSummary.aspx";
    }
}