var logger = (function(){

    var loghost = 'http://127.0.0.1/log.gif?';

    var log = function(err){

        var img = new Image(0,0);

        var _url =[];

        _url.push('name'+'='+encodeURIComponent(err.name));

        _url.push('message'+'='+encodeURIComponent(err.message));

        _url.push('location'+'='+encodeURIComponent(err.location));

        if(err.line)

            _url.push('line'+'='+encodeURIComponent(err.line));

        if(err.func)

            _url.push('func'+'='+encodeURIComponent(err.func));

        var url = _url.join('&');

        img.src = loghost+url;

        console.log(img.src);

    }

    return {log:log};

})();

function trapError(msg, URI, ln) {

    // wrap our unknown error condition in an object

    var error = new Error(msg);

    error.location = URI; // add custom property

    error.line = ln;

    logger.log(error);

    warnUser();

    return true; // stop the yellow triangle

}

window.onerror = trapError;

function foo() {

    try {

        riskyOperation();

    } catch (err) {

        // add custom property

        err.location = location.href;

        err.func = 'foo';

        logger.log(err);

        warnUser();

    }

}

function warnUser() {

    alert("An error has occurred while processing this page.\

        Our engineers have been alerted!");

    // do something

}

foo();