StaticdefaultThe recommended default level.
StaticnumericInternal numerical values for the log level.
StaticnumericThe value used for the undefined log level (maximum value).
StaticnumericThe value used for the always case (minimum value).
Protected Readonly Internal_consoleThe console object used to output the log messages.
ProtectedlevelThe numerical value of the log level.
ProtectedlevelThe name of the log level.
ProtectedbufferEmpty buffer where preliminary log lines are stored until the log level is set.
Accessor to check if the log level was initialised.
If the logger was created without an explicit log level, the logger is in a preliminary state and all log lines will be stored in an internal buffer until the log level is set.
True if the level was set.
Accessor to get the log level.
A string with the log level name.
Accessor to set the log level.
If the log level is not one of the known strings, an assert will fire.
If this is the first time when the log level is set, flush the internal buffer.
A string with the new log level.
Accessor to check the log level.
True if the log level is silent or higher.
Accessor to check the log level.
True if the log level is error or higher.
Accessor to check the log level.
True if the log level is warn or higher.
Accessor to check the log level.
True if the log level is info or higher.
Accessor to check the log level.
True if the log level is verbose or higher.
Accessor to check the log level.
True if the log level is debug or higher.
Accessor to check the log level.
True if the log level is trace or higher.
Accessor to check the log level.
True if the log level is all.
Check if the log level is set to a given level name.
This is a more generic version of the accessors (like isDebug, etc),
to be used when the log level is not know at compile time.
It can also be used to ensure that the log level is not decreased, for example:
The name of the log level.
True if the current log level is equal to the given level or higher.
Create a Logger instance.
The typical use case is to create a logger with a given log level,
usually info.
const log = new Logger({
level: 'info'
})
By default, the system console is used.
The complete use case is to create the logger instance with both a
console and a level. This might be particularly useful in tests,
where a mock console can be used to capture log messages.
const log = new Logger({
console: mockConsole,
level: 'info'
})
If present, the console must be an object derived from the
node Console, possibly with some methods overridden.
The level property is optional since it can be set later.
Without it, the constructor will
create the logger in a preliminary state, and all log lines will be stored
in an internal buffer until the log level is set.
const log = new Logger()
The generic object used to pass parameters to the constructor.
Optionallevel?: LogLevelThe name of the log level; if not passed, the logger is created in a preliminary state, and all log lines will be stored in an internal buffer, until the log level is set. Optional.
Optionalconsole?: ConsoleThe underlying console object used to log the message.
Optional. If not passed, the JavaScript standard console object
is used.
Accessor to get the underlying console object.
Direct access to the console object is useful in tests, when the console is a mock object, which allows to check the logged messages.
The console object used by the logger.
Always log a message, regardless of the log level, (even 'silent',
when no other messages are logged).
The message is passed via console.log().
Message to log, as accepted by util.format().
Rest...args: any[]Optional variable arguments.
Log an error message, if the log level is error or higher.
The message is prefixed with error: and
passed via console.error().
There is a special case when the input is an Error object. It
is expanded, including a full stack trace, and passed via
console.error().
try {
// ...
} catch (err) {
log.error(err)
}
Message to log, as accepted by util.format().
Rest...args: any[]Optional variable arguments.
Log an error message, if the log level is error or higher.
It differs from error() by not prefixing the string with error:
and using console.log() instead of console.error().
There is a special case when the input is an Error object. It
is expanded, including a full stack trace, and passed via
console.log().
try {
// ...
} catch (err) {
// Do not show the stack trace.
log.output(err)
}
Message to log, as accepted by util.format().
Rest...args: any[]Optional variable arguments.
ProtectedwriteThe internal log writer.
If the log level was defined, call the actual logger function, otherwise store the log lines in the array buffer, for later processing, when the log level is finally defined.
The log numeric level.
The function to be used to write the message.
The log message.
The Logger class implements the logger functionality.
The logger is constructed on top of a console object, where the messages are logged.
Use
log.always()instead of theconsole.log(), since it accounts for different contexts, created for example when using REPL.There is no
criticallevel, corresponding to errors that prevent the program to run, since these are actually related to bugs; useassert()instead.The messages may include formatting directives, with additional arguments, as defined by the Node.js console (not really necessary with ES6).
All output functions accept an optional string message and possibly some arguments, as processed by the standard Node.js
util.format(msg, ...args)function.If the logging code is more complex than a single line, for example if it needs a long loop, it is recommended to explicitly check the log level and, if not high enough, skip the code entirely.
There are cases when the logger must be created very early in the life cycle of an application, even before it is practically possible to determine the log level.
For these cases, if the logger is created without a log level, it is set to a preliminary state, and all log lines are stored in an internal buffer, until the log level is set, when the buffer is walked and the lines are processed.