Caipora

A full replacement of Node.js console with support to log levels.

Installation

npm install caipora

API

If you are familiar with console and its methods, this library introduces two methods to take logging to the next level.

Supported log levels

These log levels are supported: trace, debug, info, warn, error, and silent. They are defined from the smallest to the highest priority.

For example, setting to warn will disable trace, debug, and info.

By default, caipora will set the log level to info.

New methods

setLevel()

The method setLevel(level) is introduced to change the current log level. Its only argument level is case insensitive, thus calling it with debug or DEBUG will have the same outcome.

It won't fail for an unknown level. It will assume the desired log level is silent instead.

getLevel()

The method getLevel() is introduced to retrieve the current log level. The returned value is one of the supported log levels listed above.

It always returns a lowercased string. For example, if you invoked setLevel() with DEBUG, getLevel() will return debug.

Behavior of log()

Similar to console, caipora has a method associated with each log level, thus caipora.debug() is associated with the debug level.

If you want to log a message regardless of the current log level, you should use log(). It will always log even if the current log level is silent.

How to use

There are three ways to consume this library, which will be explained individually:

• Replace console with caipora completely;
• Import caipora wherever you need to add log levels;
• Creating a customized logger with caipora.Caipora;

Replacing global console

This is the recommended way if you want to add log levels to your whole application with a single line of code. Place this line as the first or one of the first lines of your application:

require("caipora/register");

or

import "caipora/register";

From now on, you can invoke any of the console or caipora methods directly from global console.

For example:

import "caipora/register";

console.debug("Hello World!"); // It does nothing because current level is "info"
console.setLevel("debug"); // It changed log level from "info" to "debug"
console.debug("Hello World!"); // It outputs "Hello World!\n" on the standard output (STDOUT)

It also provides a way to revert the replacement by importing caipora/unregister instead.

Importing caipora selectively

If you want to add log levels only to parts of your application, you should import caipora only to the modules you need. You can achieve this by adding this line of code:

var console = require("caipora");

or

import * as console from "caipora";

Please note that setting the level in a module will affect the others. Its behavior is similar to the global console although it is scoped to the modules that it has been imported.

Example:

// From file1.js where caipora is imported
import * as console from "caipora";

console.setLevel("error"); // It changed log level from "info" to "error"
console.info("Hello World!"); // It does nothing

// From file2.js where caipora is not imported
console.info("Hello World!"); // It outputs "Hello World!\n" on STDOUT

Creating a customized logger

If you want to create isolated loggers or output to different streams (such as files), you should create a new instance of caipora with caipora.Caipora.

For example:

import { Caipora } from "caipora";

let errorLogger = new Caipora(process.stderr);
errorLogger.info("This message will go to the error output.");

If you wonder what constructors are available, you should look at the official API of Console.

For compatibility reasons, caipora also exports a Console class, but it is just an alias of Caipora.

Additional features

Lazy evaluation

Caipora does introduce lazy evaluation to log messages. It is recommended for any message that contains CPU-intensive computed parameters.

In order to use this, pass a function that returns either a value or an array of values. It does support formatted messages when an array is returned.

For example:

import * as console from "caipora";

let complexObject = {
    id: "ab23af96",
    timestamp: 123456123
};
console.error(() => JSON.stringify(complexObject));
// It outputs '{"id":"ab23af96","timestamp":123456123}' on STDERR

console.error(() => ["Failed for %s", JSON.stringify(complexObject)]);
// It outputs 'Failed for {"id":"ab23af96","timestamp":123456123}.' on STDERR

Cleaner results in tests reports

If you require caipora and set your log level to silent while running tests with Mocha or Jest, you can supress all console messages from the output, making it cleaner.

For example:

LOG_LEVEL=silent mocha --require caipora/register 'test/**/*.test.js'

Typescript friendly

This library defines and exports all of its types. For example:

import { Caipora, LogLevel } from "caipora"

let logger: Caipora;

function createLogger(defaultLevel?: LogLevel) {
    logger = new Caipora(process.stdout)
    if (defaultLevel) logger.setLevel(defaultLevel)
}

export function init() {
    createLogger(process.env.NODEJS_LOG_LEVEL)
    logger.debug('Created')
}

License

MIT