JavaScript logging redone

JSNLog.js is a tiny JavaScript logging library, simple and well documented. It has unique options to cut down on the amount of logging data you receive while still getting the information you actually need.

Vital Stats

  • Supports IE 8+, Firefox, Chrome, Opera, Safari (desktop/mobile).
  • Free, open source (Apache License, Version 2.0).
  • Use stand alone, as an AMD module or CommonJS module.
  • 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

JL().setOptions(
        { "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

JL("jsLogger").setOptions(
        { "disallow": "suppress me" });

Limit total messages sent to server

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

Reduce AJAX requests by batching log messages

appender.setOptions(
        { "batchSize": 3 });

Easily send logging data to the server

Built in AjaxAppender uses simple, well documented message format.

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 with one line of code.

screenshot of browser console with log generated by JSNLog