A NodeJS logging wrapper providing transcript capabilities.
npm install @apigrate/loggerA simple logging utility, withi minimal dependencies capable of holding a transcript in memory until cleared.
By default, this logger logs to an internal NodeJS console object. The internal console object is exposed for access.
Note: this library requires NodeJS 10.x or greater
``javascript
const Logger = require('@apigrate/logger')
let logger = new Logger(logLevel, opts);
`
In the above, logLevel may be one of:
1. error show only errorswarn
1. show errors and warningsinfo
1. informational level logging, in addition to the abovedebug
1. detailed logging (typically not used in production environments), in addition to the abovetrace
1. even higher level of logging than debug (will not be output for injected winston loggers)
A basic example of output:
`javascript
let logger = new Logger('info');
logger.error('This is an error message');
logger.warn('This is a warning message');
logger.info('This is an informational message');
logger.debug('This is debugging information');
logger.trace('This is some very detailed output seldom seen');
`
...would producetext`
ERROR: This is an error message
WARN: This is a warning message
INFO: This is an informational message
because the debug and trace messages are below the logging level of 'info'.
parameter is optional. It contains the following options:omitLogLevelPrefix (boolean)
Note that the the log level prefix (e.g.
INFO: , DEBUG: ,ERROR: , etc.) is prepended to messages by default. Use the omitLogLevelPrefix to omit these prefixes when using the logger.`javascript
let logger = new Logger('info', {omitLogLevelPrefix: true});logger.info('The quick brown fox jumped over the lazy dog.');
`
...would produce
text
The quick brown fox jumped over the lazy dog.
`prefix (string)
Adds an additional prefix to each logging message.
javascript
let logger = new Logger('info', {prefix: "-->"});logger.info('The quick brown fox jumped over the lazy dog.');
`
...would produce
text
INFO: -->The quick brown fox jumped over the lazy dog.
`maxMessages (number)
The maximum number of messages the logger saves in memory. When it is exceeded, the logger emits an "overflow"
event, whose payload is the current internal transcript (i.e. string array of log messages). After this event is emitted, the logger
internally clears out the oldest message to keep the number of array elements held internally no larger than this
value.useSymbols (boolean)
Defaults to false. If true, the log level labels are replaced by symbols:
✖=error, ▲=warning, ◦=info, ▽=debug, ◇=tracesilent (boolean):
Defaults to false. If true, output is never logged to console. Use this if you are only interested in using the logger to build a transcript (see below).
events (boolean):
Defaults to false. If true, a logging event named 'log' is emitted with
{level, indent, message} as payload for each message.For example, you could use this to write your own event-driven transport function
`javascript
logger = new Logger(5, {useSymbols: true, events: true, silent: true});
logger.on('log', ({level, indent, message})=>{
let indentation = ''
for(let i=0; i${indentation} ${message});
});
` Transcript Output
A distinguishing feature of this logger library is to provide transcript output when needed. This allows the logger to accumulate a series of log messages and then output this series as newline delimited text. This can be useful if you need a processing transcript output to an external source where piping output is not an option.
`javascript
let logger = new Logger('info');
//...
logger.info('Now processing widget X.');
//...
logger.debug('Current memory footprint is 123478 bytes');
//...
logger.warn('You are getting close to your transaction limit.');
//...
logger.error('Error processing widget X. Server returned 502 indicating it is too busy.');//...
hypotheticalNotificationService.send( logger.transcript() )
`
In this case, would output:
`text
INFO: Now processing widget X.
WARN: You are getting close to your transaction limit.
ERROR: Error processing widget X. Server returned 502 indicating it is too busy.
`Logger stores these messages in memory. Which means you'll want to consider the following:
1. think about when you instantiate this Logger, it may make sense to only use it inside transaction processing blocks where you need a transcript of processing for a transaction.
1. if re-using the logger, use the