Log JavaScript client side events in your server side logs

This JavaScript logging package logs JavaScript errors, AJAX timeouts and other client side events in your server side log. Supports Elmah, Log4Net, NLog, Serilog, Common.Logging.

Why use JSNLog

  • You probably log server side events using a logging package such as Log4Net, Elmah, or NLog.
  • However, you're not logging JavaScript events. Missing out on exception information makes fixing bugs in live JavaScript code much harder.
  • Fix this by installing JSNLog.
  • Now you can add logging to your JavaScript:
    window.onerror = function (msg, url, line, col, exception) {
        JL().fatalException(msg, exception);
    }
  • JSNLog sends the log data to the server and into your server side log.
  • Your logs now have both the server and client side events. You can correlate them with request ids.
  • Install JSNLog

Demos and sample code

6 minute introduction

Vital Stats

Log important JavaScript events

Insert loggers in your JavaScript

JL().info("log message");

Optionally use logger names

JL("jsLogger").info("log message");

Log JavaScript exceptions, with their stack traces

try {
        ...
    } catch(e) {
        JL().fatalException("Exception info", e);
    }

Configure loggers in your web.config

<logger name="jslogger" level="FATAL" />

Or in server side code

loggers = new List
{
    new Logger { name = "jsLogger", level = "FATAL" }
}

Or configure them in your JavaScript code

JL("jsLogger").setOptions({ "level": 4000 });

Log objects as well as strings

var obj = {"f1": "v1", "f2": "v2"};
    JL().log(2500, obj);

Pass in function that returns log info

JL().log(2500, function() {
        // Only executed when log info
        // will actually be logged.
        var loginfo = expensiveOperation();
        return loginfo;
    });

See which messages belong to the same request

Request IDMessage
CB0734CE....A debug message
D623A22B....An error message
CB0734CE....Some other message
D623A22B....Yet another message
D623A22B....A fatal message
...

Use a single logging end point for multiple sites

<jsnlog defaultAjaxUrl="http://my-api-domain.com/jsnlog.logger"
  corsAllowedOriginsRegex="^http://my-xyz-domain[.]com$">
</jsnlog>

Filter out what you don't need

Only log high severity messages

// Only log messages with severity ERROR or higher
<logger level="ERROR" />

Suppress messages that match a regular expression

<logger disallow="suppress me" />

Only log for certain user agents or IP addresses

<logger userAgentRegex="MSIE 7|MSIE 8" />

Limit total messages sent to server

<jsnlog maxMessages="3">

Reduce AJAX requests by batching log messages

<ajaxAppender name="appender1" batchSize="3"/>

Suppress duplicate messages

LoggerMessage
jsLoggerx too high (x = 5)
jsLoggerx too high (x = 6)
jsLoggerx too high (x = 7)
jsLoggerx too high (x = 8)
jsLoggerx too high (x = 9)

Get the info you need, but only when you need it

  • To solve JavaScript exceptions, you often need to know what happened before they happened.
  • But you don't want to send trace messages with that context unless there actually is an exception.
  • Solution: JSNLog lets you buffer log messages on the client, and only send them when there is a fatal message.

Show log data in the console

Switch console logging on or off in one central location.

screenshot of browser console with log generated by JSNLog