log4
(name may be subject to change)
Universal logger utility
Configurable, environment and presentation agnostic, with log levels and namespacing (debug style) support
Usage
Writing logs
// Default logger writes at 'debug' levelconst log = ; // Log 'debug' level message:; // Get namespaced logger (debug lib style)log = log; // Log 'debug' level message in context of 'my-lib' namespace:; // Namespaces can be nestedlog = log; // Log 'debug' level message in context of 'my-lib:func' namespace:; // Log 'error' level message in context of 'my-lib:func' namespace:log; // log output can be dynamically enabled/disabled during runtimeconst restore = logerror;log;// Restore previous logs visibiity state;log;
Available log levels
Mirror of syslog (in severity order):
debug
- debugging informationinfo
- a purely informational messagenotice
- condition normal, but significantwarning
(also aliased aswarn
) - condition warningerror
- condition errorcritical
- condition criticalalert
- immediate action requiredemergency
- system unusable
Output message formatting
log4
doesn't force any specific arguments handling. Still it is recommended to assume printf-like message
format, as all available writers are setup to support it. Placeholders support reflects one implemented in Node.js format util
Excerpt from Node.js documentation:
The first argument is a string containing zero or more placeholder tokens. Each placeholder token is replaced with the converted value from the corresponding argument. Supported placeholders are:
%s
- String.%d
- Number (integer or floating point value).%i
- Integer.%f
- Floating point value.%j
- JSON. Replaced with the string '[Circular]' if the argument contains circular references.%o
- Object. A string representation of an object with generic JavaScript object formatting. Similar to util.inspect() with options { showHidden: true, depth: 4, showProxy: true }. This will show the full object including non-enumerable symbols and properties.%O
- Object. A string representation of an object with generic JavaScript object formatting. Similar to util.inspect() without options. This will show the full object not including non-enumerable symbols and properties.%%
- single percent sign ('%'). This does not consume an argument.
Note to log writer configuration developers: For cross-env compatibiity it is advised to base implementation on sprintf-kit
Enabling log writing
log4
on its own doesn't write anything to the console on any other mean (it just emits events to be consumed by preloaded log writers)
To have logs written, the pre-chosen log writer needs to be initialized in main (starting) module of a process.
List of available log writers
log4-nodejs
- For typical Node.js processeslog4-aws-lambda
- For AWS lambda environment
Note: add any new writers via PR
Logs Visibility
Default visibility depends on the enviroment (see chosen log writer for more information), and in most cases is setup through following environment variables:
LOG_LEVEL
(defaults to notice
) Lowest log level from which (upwards) all logs will be exposed.
LOG_DEBUG
Eventual list of namespaces to expose at levels below LOG_LEVEL
threshold
List is comma separated as e.g. foo,-foo:bar
(expose all foo
but not foo:bar
).
It follows convention configured within debug. To ease eventual migration from debug, configuration fallbacks to DEBUG
env var if LOG_DEBUG
is not present.
Tests
$ npm test
Project cross-browser compatibility supported by: