A very simple logging library for node.js
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README.md
index.js
package.json
test.js

README.md

node-lumberjack

A very simple logging library for node.js

Features

  • Supports the %s format string - use it for every argument. If the parameter is not a string, it is converted to one using String(object)

  • Prints:

    • Timestamp
    • Log Statement Severity
    • Module Name
    • Constructor name
    • Function name
    • Line number
  • A logger object (returned by getLogger) supports the following methods:

    • trace
    • debug
    • info
    • warn
    • error
    • fatal
    • getLevel(): Returns the currently set log level
    • setLevel(levelString): Sets the current log level
  • trace is the most verbose log level and fatal is the least. If you set the log level to info, then all log statements between levels fatal and info (both inclusive) will be logged.

  • More generally, if you set the logging level to X, then all log statements between fatal and X (both inclusive) will be logged.

Caveats

The performance of node-lumberjack (or any logging module that shows the line number/module name/function name) is going to be worse than that of a logging module that does not. This difference is pretty pronounced if you indulge in a lot of logging. By a lot of logging, I mean many calls to one of the logging functions rather than logging a lot of data per line. In some simple tests I ran, the performance difference was 3 sec without printing line numbers and 15 sec with them. This is a 5x difference, and you might not want to pay this penalty.

node-lumberjack does NOT currently give you an option to turn off line numbers since I feel that line numbers are crucial to help in debugging errors (which is one of the major use-cases for logging). If you do not wish to pay this penalty, choose an appropriate logging module from this list.

Example usage

var path     = require('path');
var filename = path.basename(path.normalize(__filename))
var log      = require('node-lumberjack').getLogger(filename, 'trace');

log.info("Line 1");
log.warn("Line %s", 2);

See the file test.js for a complete example on how to use this library.

Example output

[2012-06-10 12:14:23.350] [INFO] [test.js:test:7] - Line 1
[2012-06-10 12:14:23.359] [WARN] [test.js:test:8] - Line 2
[2012-06-10 12:14:23.359] [DEBUG] [test.js:test:9] - 3rd line
[2012-06-10 12:14:23.360] [ERROR] [test.js:test:10] - 4th Line comes here
[2012-06-10 12:14:23.360] [TRACE] [test.js:test:11] - Tracing on the 5th line

node-lumberjack prints the module name, constructor name, function name and the line number on which the logging function was called. Here is an example:

[2012-06-10 12:14:23.362] [TRACE] [test.js:CtorName.functionName:20] - You should see the object & function name on this line