Node.js log4js Notes

Sep 24, 2024#log4js50

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**Introduction** In the fields of security and development, logs can reveal ongoing security risks, performance issues, and various events, aiding in program improvement and testing. They allow for easy identification of problem causes and quick modifications. **Quick Start** Refer to the official log4js documentation: https://log4js-node.github.io/log4js-node/. Basic usage involves using the logger to print a string by calling `getLogger` to obtain a logger instance: ```javascript const log4js = require('log4js'); const logger = log4js.getLogger(); logger.debug('This is a test message'); ``` **Log Levels** Logs have different levels, ranked from low to high as follows: 1. TRACE 2. DEBUG 3. INFO 4. WARN 5. ERROR 6. FATAL 7. MARK **Categories** In log4js, the concept of categories allows you to see the source module of the logs or customize configurations: ```javascript const log4js = require('log4js'); const logger = log4js.getLogger('abc'); logger.debug('The logger type is abc'); ``` **Appenders** To output logs to a file or customize configurations, you can set up an Appender. By default, all logs are output to the console: ```javascript defaultConfig = { appenders: [{ type: "console" }] } ``` You can create your own Appender configuration using log4js's configuration method: ```javascript log4js.configure({ appenders: { out: { type: 'stdout' }, info: { type: 'file', filename: 'logs/info.log', maxLogSize: 52428800 } } }); ``` **Under Construction...**

Introduction#

In the fields of security and development, logs can reflect ongoing potential security risks, performance issues, and various events, which are beneficial for program improvement and testing.

Through logs, we can easily identify the causes of problems afterward and quickly make modifications to the source of the issues.

Quick Start#

Official documentation for log4js: https://log4js-node.github.io/log4js-node/

Basic usage method, using logger to print a string, and calling getLogger to obtain an instance of the logger:

const log4js = require('log4js')
const logger = log4js.getLogger()
logger.debug('This is a test message')

Log Levels#

Logs have different levels, each with different weights, from low to high:

1: TRACE
2: DEBUG
3: INFO
4: WARN
5: ERROR
6: FATAL
7: MARK

Type#

In log4js, there is a concept of category (type), which allows you to see which module the logs are coming from, or to configure custom types.

const log4js = require('log4js')
const logger = log4js.getLogger('abc')
logger.debug('At this point, the logger type is abc')

Appender#

If you want to output logs to a file or customize some configurations, you can configure the Appender to accomplish this.

Below is the default Appender configuration for log4js; by default, all logs will be output to the console:

defaultConfig = {
  appenders: [{
    type: "console"
  }]
}

You can also create your own Appender configuration using log4js's configuration method:

log4js.configure({
    appenders: {
        out: {
            type: 'stdout'
        },
        info: {
            type: 'file',
            filename: 'logs/info.log',
            maxLogSize: 52428800
        }
    }
})

Under construction...