We are moving

Now that Googlecode is out, we have had to find a new Log4js-ext home.

However, we will keep this website as is for reference

New in log4js-ext 2.0...

Log4js-ext 2.0 is out!

This version adds support for remote logging and an enhanced log viewer window that adds search & highlight capabilities.

Besides, the API documentation is now available online.

What is log4js-ext?

log4js-ext is a Javascript logging system with features that closely resemble those of the popular log4j or slf4j libraries, and works in the ExtJs ecosystem.

If you are familiar with log4j or any of the manylibraries inspired by it, you will be able to put log4js-ext to work immediately.

Hello world

Just to give you a glimpse, here is a little code that shows from simpler to more advanced logging:

```javascript

logger = Sm.log.Logger.getLogger('Sm.log.example1'); // A simple log logger.info( "Information message");

// Formatted log logger.warn( "Message, level={0} (text substitutions={1})", "WARN", 2);

// Even more advanced formatting logger.error( "Message, level={type} (text substitutions={count})", {type: "ERROR", count: 2});

// Log an object, so that we can later take a look at it obj = { name: 'John', dog: {name: 'Spottie', hair: 'brown'}, ratings: [2500]}; logger.debug( {msg: 'Logged an object...', loggedObject: obj});

```

You have probably noticed the {0} or {count} parameters used to format log messages in an easy way.

Besides, in the logger.debug call, we have a mysterious loggedObject, which is the way to log arbitrary objects so that we can peruse them later.

How will this look like? Well, if you use the window based log4js-ext log viewer you'll get this,

Of course, you can sort and filter logs by priority, category, message contents and even a value in the logged object.

For example, if you set the Logged Object filter to 'John', you will see just the fourth log. A neat way to find your way through tons of log entries!

If you prefer to use your browser console for log output, you will get something like this:

log4js-ext provides almost all functionality users of logging libraries such as log4j have come to expect, including hierarchical loggers, customizable appenders that can allow you to send log information to a remote server, customizable formatting, etc.

If you are not familiar with those libraries, you need not worry: log4js-ext is very easy to use and learn by doing.

Main features of log4js-ext

I created this logging system for personal use because I needed a logging library, that provided all of the following functionality:

• It was a must to have a good GUI based viewer that allowed me to filter logs by different criteria: category, priority (info, error, debug, warn...), message content, etc.

• I needed some way to group related logs so that I could distinguish what logs were part of a certain complex operation. I decided to support the NDC concept Log4j supports. Of course, the GUI viewer allows NDC filtering

• I needed to log arbitrary objects at some moment, and see them as nicely highlighted JSON. And, of course, log4js-ext should allow searching any value in the logged objects.

• I needed an easy way to format log messages, avoiding hand-made concatenations and formating as much as possible.

• I wanted it to be extensible, meaning I should be able to add support for things such as remote logging, to define new ways to format messages, etc.

• I wanted it to be easy to use and familiar to users of popular log libraries for other languages, such as log4j, logback, etc. Log4js-ext closely resembles log4j.

• And, of course, I needed robustness. This means, among other things, lots of automated JsTestDriver tests.

Log4js-ext fulfills all these goals, and since I'm quite happy with the outcome, I felt it would be nice to contribute it to the community, much as I did with my DirectJNgine project.

Putting log4js-ext to work

After installing the library you will want to take a look at logging basics to get started. There you fill find information about advanced formatting, too.