Javascript Error Logging with Elmah

var BaseUrl = window.location.protocol + "//" + window.location.host + "/";
var APIUrl = BaseUrl + "api/";
var errorsAPIUrl = APIUrl + "errors/";

Function.prototype.trace = function () {
    var trace = [];
    var current = this;
    while (current) {
        trace.push(current.signature());
        current = current.caller;
    }
    return trace;
};

Function.prototype.signature = function () {
    var signature = {
        name: this.getName(),
        params: [],
        toString: function () {
            var params = this.params.length > 0 ?
                "'" + this.params.join("', '") + "'" : "";
            return this.name + "(" + params + ")";
        }
    };
    if (this.arguments) {
        for (var x = 0; x < this.arguments.length; x++)
            signature.params.push(this.arguments[x]);
    }
    return signature;
};

Function.prototype.getName = function () {
    if (this.name)
        return this.name;
    var definition = this.toString().split("\n")[0];
    var exp = /^function ([^\s(]+).+/;
    if (exp.test(definition))
        return definition.split("\n")[0].replace(exp, "$1") || "anonymous";
    return "anonymous";
};

window.onerror = function (msg, url, line) {
    if (arguments != null && arguments.callee != null && arguments.callee.trace)
        logError(msg, arguments.callee.trace());
};

function logError(ex, stack) {
    if (ex == null) return;
    if (errorsAPIUrl == null) {
        alert('errorsAPIURL must be defined.');
        return;
    }

    var url = ex.fileName != null ? ex.fileName : document.location;
    if (stack == null && ex.stack != null)
        stack = ex.stack;

    // format output
    var out = ex.message != null ? ex.name + ": " + ex.message : ex;
    out += ": at document path '" + url + "'.";
    if (stack != null) out += "\n  at " + stack.join("\n  at ");

    // send error message
    $.ajax({
        type: 'POST',
        url: errorsAPIUrl,
        data: { value: out }
    });
}