Node.js logging package for both client and server

This Node.js logging package logs JavaScript errors and other events on both client and server. Client side logs are sent to the server and logged there. On the server logs to the console, or a database using Winston transports.

Why use JSNLog

  • You probably log server side exceptions and other events using a logging package such as Winston.
  • However, you're not logging client side events. This makes fixing bugs in live client side code much harder.
  • Fix this by installing JSNLog. It automatically logs client side exceptions to your server side log.
  • And you can log other JavaScript events as well, such as AJAX timeouts:
  • 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

Vital Stats

  • Supports IE 8+, Firefox, Chrome, Opera, Safari (desktop/mobile).
  • Free, open source (MIT).
  • Use stand alone, as an AMD module or ES6 module or CommonJS module. Available on cdnjs.
  • No dependencies on other JavaScript libraries.
  • Fully documented: API docs, examples, how to's.

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 JavaScript code

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

Only log for certain user agents or IP addresses

        { "userAgentRegex": "MSIE 7|MSIE 8" });

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

Filter out what you don't need

Only log high severity messages

// Only log messages with severity ERROR or higher
JL().setOptions({ "level": JL.getErrorLevel() });

Suppress messages that match a regular expression

        { "disallow": "suppress me" });

Limit total messages sent to server

JL.setOptions({"maxMessages": 3});

Reduce AJAX requests by batching log messages

        { "batchSize": 3 });

Suppress duplicate messages

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.