medikoo
log
Universal logging utility
Configurable, environment and presentation agnostic, with log levels and namespacing (debug style) support
Usage
1. Write application/library logs
// Default logger (writes at 'info' level)
const log = require("log");
// Log 'info' level message:
log.info("some info message %s", "injected string");
// Get namespaced logger (debug lib style)
const myLibLog = log.get("my-lib");
// Log 'info' level message in context of 'my-lib' namespace:
myLibLog.info("some info message in 'my-lib' namespace context");
// Namespaces can be further nested
const myLibFuncLog = log.get("func");
// Log 'info' level message in context of 'my-lib:func' namespace:
myLibFuncLog.info("some info message in 'my-lib:func' namespace context");
// Log 'error' level message in context of 'my-lib:func' namespace:
myLibFuncLog.error("some error message");
// log output can be dynamically enabled/disabled during runtime
const { restore } = myLibFuncLog.error.disable();
myLibFuncLog.error("error message not really logged");
// Restore previous logs visibiity state
restore();
myLibFuncLog.error("error message to be logged");2. Initialize log writer in main (starting) process module
e.g. if target is Node.js, then install log-node, and at the top of main module initialize it
require("log-node")();Available log levels
Mirror of applicable syslog levels (in severity order):
debug- debugging information (hidden by default)info- a purely informational message (hidden by default)notice- condition normal, but significantwarning(also aliased aswarn) - condition warningerror- condition error - to notify of errors accompanied with recovery mechanism (hence reported as log and not as uncaught exception)
Note: critical, alert, emergency are not exposed as seem to not serve a use case in context of JS applications,
such errors should be exposed as typical exceptions
Output message formatting
log doesn't force any specific arguments handling. Still it is recommended to assume printf-like message
format, as all currently 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 compatibility it is advised to base implementation on sprintf-kit
Enabling log writing
log on its own doesn't write anything to the console or any other means (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 the main (starting) module of a process.
List of available log writers
log-node- For typical Node.js processeslog-aws-lambda- For AWS lambda environment
Note: if some writer is missing, propose a PR
Logs Visibility
Default visibility depends on the enviroment (see chosen log writer for more information), and in most cases is setup through the 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.
Timestamps logging
When following env var is set writers are recommended to expose timestamps aside each log message
LOG_TIME
rel(default) - Logs time elapsed since logger initializationabs- Logs absolute time in ISO 8601 format
Tests
$ npm testProject cross-browser compatibility supported by:
Security contact information
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