Logger Class with log levels

This is a simple logger class with nice output, similar to systemd logging in Linux.

Sample output

The logger output will look something like this::

2020-07-04T19:51:02.743Z [detail] db-one.DBGenerator.attachReverseAssociationMethods:   attaching countUserUserData(userId)
2020-07-04T19:51:02.744Z [MODULE] db-one.DBEnv: Written class code for _user (28889 bytes) to generated/GeneratedUserSession.js
                                  you can extend this class or use it as it is
2020-07-04T19:51:02.744Z [MODULE] db-one.DBEnv: Setting session classes in session factory objects
2020-07-04T19:51:02.745Z [ INFO ] db-one.DBLiveContext.initFactory: Initialising factory object
2020-07-04T19:51:02.745Z [ INFO ] db-one.DBSessionFactory: Creating DBSessionFactory Object
2020-07-04T19:51:02.751Z [ INFO ] db-one.DBLiveContext.initFactory: Initialising factory object
2020-07-04T19:51:02.752Z [ INFO ] db-one.DBSessionFactory: Creating DBSessionFactory Object
2020-07-04T19:51:02.753Z [ INFO ] db-one.DBLiveContext.initFactory: Initialising factory object
2020-07-04T19:51:02.754Z [ INFO ] db-one.DBSessionFactory: Creating DBSessionFactory Object
2020-07-04T19:51:02.754Z [ INFO ] db-one.DBEnv.loadModels: Loading system specific models
2020-07-04T19:51:02.755Z [ INFO ] db-one.DBContext.loadModels: Loading Models
2020-07-04T19:51:02.755Z [ INFO ] db-one.ModelLoader.loadModels: Load Models, count = 3
2020-07-04T19:51:02.758Z [MODULE] db-one.DBEnv.connect: Connecting to database
2020-07-04T19:51:02.758Z [ INFO ] db-one.DBCore.authenticate: Authenticating to database
2020-07-04T19:51:02.864Z [ PSQL ] db-one.query: Executing (default): SELECT 1+1 AS result
2020-07-04T19:51:02.865Z [ INFO ] db-one.DBCore.initialise: Database connection to 'localhost/dbone' successful

It includes timestamps, colors for log levels and proper text indentation and wrapping. The logging entities are easily configured.

How to include

After installing via npm, use require::

const logger = require("logger-one").getInstance();

The logger uses a singleton pattern so that all settings apply throughout your entire project. However, if you want a logger that is specific to a file or module, the singleton pattern is not mandatory. You can initialize a new logger object::

const Logger = require("logger-one");

let logger = new Logger();

How to use

There are multiple log levels and corresponding functions. Calling them will create a log output similar to this::

<timestamp> [<level>] <service>.<class> <id> <log text>
                      <more log text>
                      <even more log text>

The predefined log levels and functions are:

* `detail`: lowest possible level, displays <level> in gray
* `sql`: specific log level for sql commands, displays <level> in cyan and <log text> in gray
* `info`: informative log message, displays <level> in green
* `sess`: session specific informative message, displayes <level> in green and bold
* `warn`: warning message, displayes <level> in yellow and bold
* `module`: module-level informative messages (such as "starting up"), displays <level> in green and bold and text in bold
* `error`: error message, displays <level> in red and bold

To call the function::

logger.info(text, cls, service, id)

The <id> argument is optional and can be used for session ids, for instance. Class argument can include the function as well, for instance::

logger.info("Running setup", "Application.setup", "app");

Module bindings

A module binding is a custom wrapping around the Logger instance. This is a good option if we want to preserve the singleton pattern (so, same configuration throughout the project) but have some level of customization. To get a module binding, use::

const logger = require("logger-one").getInstance().moduleBinding(cls, service);

Where cls and service are class and service names that will be used by default whenever calling a log function on the binding. So, instead of::

const logger = require("logger-one").getInstance();
logger.info("Running setup", "Application.setup", "app");

You can use a module binding in the file and only specify the function name in the log function call::

const logger = require("logger-one").getInstance().moduleBinding("Application", "app");
logger.info("Running setup", "setup");

The module binding object will only provide logging methods, so methods such as setLevel() will not work.

Configuring the logger object

If you use the singleton pattern (by calling getInstance()), configuration options will apply throughout your project.

These work only on instances obtained with getInstance() or with the constructor, they will not work on the module bindings.

This is a list of configuration methods.

setColors(arr)

Applies color settings to all log text output.

• arr: array of strings, a list of colors to apply to output log text. The options are the same used by the colors package, which this library is using

Example::

logger.setColors([ "gray", "bold" ]); // makes all output gray and bold

setLevel(level)

Sets logging level (logger instance will not display any message lower than this level).

• level: string, one of the levels specified below

Level order, from lowest to highest, is: detail, sql, info, sess, warn, module, error.

Example::

logger.setLevel("warn");
logger.info("This will not be displayed");
logger.warn("This will be displayed");
logger.error("This as well");

setConsoleWidth(width)

Sets the wrapping width in characters. The logger will automatically try to get the output width from the console, however if writing to a file this does not apply so the width will be automatically set to 260. You can call this method to change this setting.

• width: number, the wrapping width

getConsoleWidth()

Returns the current console width used by the logger.

setLogFunction()

The log function used by the logger. By default, it's the formattedOutput methods of the logger object, but you can change it to anything as long as it uses console.log() syntax (arguments will be merged together as one output line). Replacing this will, of course, remove all the neat formatting and you'll have to handle that yourself.

resetLogFunction()

Sets the log function back to the built-in default.

isActiveLevel(level)

Check if level should be displayed or not, based on the set logging level. Example::

logger.setLevel("warn");
logger.isActiveLevel("info"); // returns false
logger.isActiveLevel("warn"); // returns true
logger.isActiveLevel("error"); // returns true

Advanced logging functionality

There is some built-in functionality for logging objects and integer masks. These are implemented as static functions of the Logger class.

Logger.expand(logFn, obj, name, cls, service, id)

"Expand" an object and log all properties individually.

• logFn: the logging function to use, eg logger.info
• obj: object to display
• name: root name of the object, eg input or config
• cls, service, id: same as the logging functions

Example::

const Logger = require("logger-one");
const logger = Logger.getInstance();

let o = { a: 42, b: { c: "hello world", d: null } };
Logger.expand(logger.info, o, "obj");
// displays something like
// [ INFO ] obj.a: 42
// [ INFO ] obj.a.b.c: "hello world"
// [ INFO ] obj.a.b.d: null

Logger.mapInt (logFn, value, obj, name, cls, service, id)

Expands and logs properties defined by an int mask.

• logFn: the logging function to use, eg logger.info
• value: the int value to display as flags
• obj: an object containing keys and values for each flag
• name: root name of the object, eg input or config
• cls, service, id: same as the logging functions

Example::

const Logger = require("logger-one");
const logger = Logger.getInstance();

let allProps = { PROPERTY1: 1, PROPERTY2: 2, PROPERTY3: 4 };
let prop = allProps.PROPERTY1 | allProps.PROPERTY3;
logger.mapInt(logger.info, prop, allProps, "prop");
// displays something like
// prop.PROPERTY1: true
// prop.PROPERTY2: false
// prop.PROPERTY3: true