This document enables us to use the logging facilities that come with Cerny.js. It shows us how to obtain a logger and adjust the log level in the configuration file cerny.conf.js, so we get to see only those messages that are interesting for us.

Getting a logger

In order to output log statements, we need to obtain a logger object. We can achieve this by including the following line into our code:

OURAPP.doSomething = function() { var logger = CERNY.Logger("OURAPP.doSomething"); // do something ... logger.debug("myvar: " + CERNY.dump(myvar")); ... }


CERNY.logger takes one parameter, which is a string and is called the category of the logger. The category is a list of names separated by dots, which denote a path in a hierachy. The closer the name is to the beginning, the higher it is in the hierachy. In the configuration we can deactivate loggers on a higher level but still get the output of more specific loggers. Here is an example how the logger configuration could look like:

CERNY.Configuration = { Logger: { "OURAPP": "OFF", "OURAPP.doSomething": "DEBUG" }, ... }

Log levels

The log levels are the standard ones that are familiar from Log4j or derivates. They are OFF, FATAL, ERROR, WARN, INFO, DEBUG, and TRACE. The logger has corresponding functions in lower case letters for each of these levels. The meaning of these levels are subject to project policy. The general distinction between production levels and development levels is common. The border is usually not strictly defined. In some teams INFO is the first development level, in other teams it is DEBUG.

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