### Install log4js-node

Source: https://log4js-node.github.io/log4js-node/index.html

Install the log4js-node package using npm.

```bash
npm install log4js

```

--------------------------------

### v1 Configuration Example

Source: https://log4js-node.github.io/log4js-node/migration-guide.html

This is an example of a v1 configuration object for log4js. Note the array format for appenders.

```javascript
{
  appenders: [
    { type: "console" },
    {
      type: "dateFile",
      filename: "logs/task",
      pattern: "-dd.log",
      alwaysIncludePattern: true,
      category: "task",
    },
  ]
}
```

--------------------------------

### v2 Configuration Example

Source: https://log4js-node.github.io/log4js-node/migration-guide.html

This is an example of a v2 configuration object for log4js. Appenders are now named objects, and categories must be explicitly defined.

```javascript
{
  appenders: {
    out: { type: 'console' },
    task: {
      type: 'dateFile',
      filename: 'logs/task',
      pattern: '-dd.log',
      alwaysIncludePattern: true
    }
  },
  categories: {
    default: { appenders: [ 'out' ], level: 'info' },
    task: { appenders: [ 'task' ], level: 'info' }
  }
}
```

--------------------------------

### Configure MultiFile Appender with Log Rolling

Source: https://log4js-node.github.io/log4js-node/multiFile.html

This example demonstrates configuring the multiFile appender with log rolling and compressed backups. Logs are split by 'userID', capped at 10MB, and up to 3 compressed backups are kept.

```javascript
log4js.configure({
  appenders: {
    everything: {
      type: "multiFile",
      base: "logs/",
      property: "userID",
      extension: ".log",
      maxLogSize: 10485760,
      backups: 3,
      compress: true,
    },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});

const userLogger = log4js.getLogger("user");
userLogger.addContext("userID", user.getID());
userLogger.info("this user just logged in");

```

--------------------------------

### Configure basic stdout appender with basic layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

Configures the stdout appender to use the basic layout. This is a common setup for general logging.

```javascript
log4js.configure({
  appenders: { out: { type: "stdout", layout: { type: "basic" } } },
  categories: { default: { appenders: ["out"], level: "info" } },
});
```

--------------------------------

### Log an error message with basic layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

Demonstrates logging an error message using the basic layout. This example shows the typical output format including timestamp, level, category, and the message.

```javascript
log4js.configure({
  appenders: { out: { type: "stdout", layout: { type: "basic" } } },
  categories: { default: { appenders: ["out"], level: "info" } },
});
const logger = log4js.getLogger("cheese");
logger.error("Cheese is too ripe!");
```

--------------------------------

### Install pm2-intercom for PM2 Integration

Source: https://log4js-node.github.io/log4js-node/clustering.html

Install the pm2-intercom module to enable log4js to work correctly with PM2. This is a prerequisite for configuring log4js for PM2.

```bash
pm2 install pm2-intercom

```

--------------------------------

### Configure Synchronous File Appender

Source: https://log4js-node.github.io/log4js-node/fileSync.html

Configure the 'fileSync' appender to write all logs to a single file. This setup is suitable for basic logging needs where immediate persistence is required.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "fileSync", filename: "all-the-logs.log" },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});

const logger = log4js.getLogger();
logger.debug("I will be logged in all-the-logs.log");

```

--------------------------------

### Configure File Appender with Log Rolling and Compression

Source: https://log4js-node.github.io/log4js-node/file.html

Configure the file appender with log rolling based on size and compressed backups. This setup ensures that log files do not grow indefinitely and are stored efficiently.

```javascript
log4js.configure({
  appenders: {
    everything: {
      type: "file",
      filename: "all-the-logs.log",
      maxLogSize: 10485760,
      backups: 3,
      compress: true,
    },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});

```

--------------------------------

### Log a message with messagePassThrough layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

Logs a message using the messagePassThrough layout. This example shows how only the message data is outputted, without timestamp, level, or category.

```javascript
const logger = log4js.getLogger("cheese");
const cheeseName = "gouda";
logger.error("Cheese is too ripe! Cheese was: ", cheeseName);
```

--------------------------------

### Output of Custom JSON Layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

This is the expected output when using the custom JSON layout defined in the previous example. Note that the exact timestamp will vary.

```json
{"startTime":"2017-06-05T22:23:08.479Z","categoryName":"json-test","data":["this is just a test"],"level":{"level":20000,"levelStr":"INFO"},"context":{}},
{"startTime":"2017-06-05T22:23:08.483Z","categoryName":"json-test","data":["of a custom appender"],"level":{"level":40000,"levelStr":"ERROR"},"context":{}},
{"startTime":"2017-06-05T22:23:08.483Z","categoryName":"json-test","data":["that outputs json"],"level":{"level":30000,"levelStr":"WARN"},"context":{}},

```

--------------------------------

### Get Logger Instance

Source: https://log4js-node.github.io/log4js-node/api.html

Retrieves a logger instance for a specified category. If the logger is not configured, it defaults to 'default' category.

```javascript
const logger = log4js.getLogger('myCategory');
```

```javascript
const logger = log4js.getLogger();
```

--------------------------------

### Configure File Appender with Log Rolling

Source: https://log4js-node.github.io/log4js-node/fileSync.html

Configure the 'file' appender with 'maxLogSize' and 'backups' for log rolling. This example demonstrates how to set up automatic log file rotation when a specified size is reached, preserving a history of log files.

```javascript
log4js.configure({
  appenders: {
    everything: {
      type: "file",
      filename: "all-the-logs.log",
      maxLogSize: 10458760,
      backups: 3,
    },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});

```

--------------------------------

### Configure No-Log Filter with Multiple Exclusions

Source: https://log4js-node.github.io/log4js-node/noLogFilter.html

This example shows how to configure the no-log filter using an array of regular expressions to exclude messages. It demonstrates excluding messages containing 'NOT', digits (\d), or empty strings. Note that empty strings are ignored, and the matching is case-insensitive.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
    filtered: {
      type: "noLogFilter",
      exclude: ["NOT", "\\d", ""],
      appender: "everything",
    },
  },
  categories: {
    default: { appenders: ["filtered"], level: "debug" },
  },
});

const logger = log4js.getLogger();
logger.debug("I will be logged in all-the-logs.log");
logger.debug("I will be not logged in all-the-logs.log");
logger.debug("A 2nd message that will be excluded in all-the-logs.log");

```

--------------------------------

### Add Custom JSON Layout to Log4js

Source: https://log4js-node.github.io/log4js-node/layouts.html

Define and configure a custom JSON layout for log4js. This example shows how to register a new layout type and use it with a stdout appender. Ensure `log4js.addLayout` is called before `log4js.configure`.

```javascript
const log4js = require("log4js");

log4js.addLayout("json", function (config) {
  return function (logEvent) {
    return JSON.stringify(logEvent) + config.separator;
  };
});

log4js.configure({
  appenders: { out: { type: "stdout", layout: { type: "json", separator: "," } } },
  categories: { default: { appenders: ["out"], level: "info" } },
});

const logger = log4js.getLogger("json-test");
logger.info("this is just a test");
logger.error("of a custom appender");
logger.warn("that outputs json");
log4js.shutdown(() => {});

```

--------------------------------

### Stdout Appender with Shutdown Function

Source: https://log4js-node.github.io/log4js-node/writing-appenders.html

This example extends the basic stdout appender by adding a `shutdown` function. The `shutdown` function is called when log4js is stopping and should be used for resource cleanup. Ensure your shutdown function accepts a callback.

```javascript
// This is the function that generates an appender function
function stdoutAppender(layout, timezoneOffset) {
  // This is the appender function itself
  const appender = (loggingEvent) => {
    process.stdout.write(`${layout(loggingEvent, timezoneOffset)}\n`);
  };

  // add a shutdown function.
  appender.shutdown = (done) => {
    process.stdout.write("", done);
  };

  return appender;
}

// ... rest of the code as above

```

--------------------------------

### Configure Category Filter Appender

Source: https://log4js-node.github.io/log4js-node/categoryFilter.html

Use this configuration to set up a categoryFilter appender that excludes logs from 'noisy.component' and directs all other logs to 'all-the-logs.log'. This setup is beneficial when you need to isolate logs from specific noisy parts of your application.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
    "no-noise": {
      type: "categoryFilter",
      exclude: "noisy.component",
      appender: "everything",
    },
  },
  categories: {
    default: { appenders: ["no-noise"], level: "debug" },
  },
});

const logger = log4js.getLogger();
const noisyLogger = log4js.getLogger("noisy.component");
logger.debug("I will be logged in all-the-logs.log");
noisyLogger.debug("I will not be logged.");

```

--------------------------------

### Configure Log Level Filter Appender

Source: https://log4js-node.github.io/log4js-node/logLevelFilter.html

Use this configuration to filter log events based on their level. Events within the specified 'level' and 'maxLevel' range are sent to the wrapped appender. This example sends 'error' and 'fatal' events to 'panic-now.log' while all events go to 'all-the-logs.log'.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
    emergencies: { type: "file", filename: "panic-now.log" },
    "just-errors": {
      type: "logLevelFilter",
      appender: "emergencies",
      level: "error",
    },
  },
  categories: {
    default: { appenders: ["just-errors", "everything"], level: "debug" },
  },
});
```

--------------------------------

### Configure No-Log Filter with Single Exclusion

Source: https://log4js-node.github.io/log4js-node/noLogFilter.html

This example demonstrates how to configure the no-log filter to exclude messages containing the string 'not'. Ensure the 'noLogFilter' type is specified, along with the 'exclude' pattern and the target 'appender'.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
    filtered: {
      type: "noLogFilter",
      exclude: "not",
      appender: "everything",
    },
  },
  categories: {
    default: { appenders: ["filtered"], level: "debug" },
  },
});

const logger = log4js.getLogger();
logger.debug("I will be logged in all-the-logs.log");
logger.debug("I will be not logged in all-the-logs.log");

```

--------------------------------

### Handle File Appender Memory Usage

Source: https://log4js-node.github.io/log4js-node/file.html

Listen for 'log4js:pause' events to manage memory usage when the file appender starts buffering logs. Stop logging when 'true' is received and resume when 'false' is received.

```javascript
log4js.configure({
  appenders: {
    output: { type: "file", filename: "out.log" },
  },
  categories: { default: { appenders: ["output"], level: "debug" } },
});

let paused = false;
process.on("log4js:pause", (value) => (paused = value));

const logger = log4js.getLogger();
while (!paused) {
  logger.info("I'm logging, but I will stop once we start buffering");
}

```

--------------------------------

### Configure Default and Appenders with Categories

Source: https://log4js-node.github.io/log4js-node/categories.html

Sets up stdout and file appenders, defining default and 'app' categories with trace level. Use this to establish basic logging configurations.

```javascript
const log4js = require("log4js");
log4js.configure({
  appenders: {
    out: { type: "stdout" },
    app: { type: "file", filename: "application.log" },
  },
  categories: {
    default: { appenders: ["out"], level: "trace" },
    app: { appenders: ["app"], level: "trace" },
  },
});

const logger = log4js.getLogger();
logger.trace("This will use the default category and go to stdout");
const logToFile = log4js.getLogger("app");
logToFile.trace("This will go to a file");

```

--------------------------------

### Configure and Use Connect Logger

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Set up log4js with console and file appenders, then use connectLogger to log requests to a specific logger. Requires express and log4js.

```javascript
var log4js = require("log4js");
var express = require("express");

log4js.configure({
  appenders: {
    console: { type: "console" },
    file: { type: "file", filename: "cheese.log" },
  },
  categories: {
    cheese: { appenders: ["file"], level: "info" },
    default: { appenders: ["console"], level: "info" },
  },
});

var logger = log4js.getLogger("cheese");
var app = express();
app.use(log4js.connectLogger(logger, { level: "info" }));
app.get("/", function (req, res) {
  res.send("hello world");
});
app.listen(5000);

```

--------------------------------

### Basic stdout Appender Configuration

Source: https://log4js-node.github.io/log4js-node/writing-appenders.html

This code defines the `configure` function for a simple stdout appender. It demonstrates how to load a layout and return the appender function. Use this as a template for creating custom appenders.

```javascript
// This is the function that generates an appender function
function stdoutAppender(layout, timezoneOffset) {
  // This is the appender function itself
  return (loggingEvent) => {
    process.stdout.write(`${layout(loggingEvent, timezoneOffset)}\n`);
  };
}

// stdout configure doesn't need to use findAppender, or levels
function configure(config, layouts) {
  // the default layout for the appender
  let layout = layouts.colouredLayout;
  // check if there is another layout specified
  if (config.layout) {
    // load the layout
    layout = layouts.layout(config.layout.type, config.layout);
  }
  //create a new appender instance
  return stdoutAppender(layout, config.timezoneOffset);
}

//export the only function needed
exports.configure = configure;

```

--------------------------------

### Configure stdout and file appenders

Source: https://log4js-node.github.io/log4js-node/appenders.html

Define 'out' for standard output and 'app' for file logging. Set the default category to use both with debug level.

```javascript
const log4js = require("log4js");
log4js.configure({
  appenders: {
    out: { type: "stdout" },
    app: { type: "file", filename: "application.log" },
  },
  categories: {
    default: { appenders: ["out", "app"], level: "debug" },
  },
});

```

--------------------------------

### Configure Hourly Log Rolling with Compressed Backups

Source: https://log4js-node.github.io/log4js-node/dateFile.html

Configure hourly log rolling with compressed backups. Log files are renamed and compressed with a `.gz` extension each hour.

```javascript
log4js.configure({
  appenders: {
    everything: {
      type: "dateFile",
      filename: "all-the-logs.log",
      pattern: "yyyy-MM-dd-hh",
      compress: true,
    },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});
```

--------------------------------

### log4js.configure(object || string)

Source: https://log4js-node.github.io/log4js-node/api.html

Configures the log4js library. Accepts a configuration object directly or a string path to a JSON configuration file. Configuration should be done early in the application lifecycle. If using `cluster`, configure in worker processes as well.

```APIDOC
## POST /log4js.configure

### Description
Configures the log4js library with a given configuration object or a file path.

### Method
POST

### Endpoint
/log4js.configure

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
- **config** (object | string) - Required - The configuration object or a string path to a JSON configuration file.

### Request Example
```json
{
  "config": {
    "levels": {
      "custom": {"value": 1337, "colour": "blue"}
    },
    "appenders": {
      "out": {"type": "stdout", "layout": {"type": "pattern", "pattern": "%[[%date] %-5level%] %-10category : %m%n%s"}},
      "app": {"type": "file", "filename": "all-the-logs.log"}
    },
    "categories": {
      "default": {"appenders": ["out"], "level": "INFO"},
      "http": {"appenders": ["out", "app"], "level": "DEBUG"}
    }
  }
}
```

### Response
#### Success Response (200)
- **log4js_object** (object) - The configured log4js object.

#### Response Example
```json
{
  "message": "Configuration successful"
}
```
```

--------------------------------

### Configure Categories with Inheritance

Source: https://log4js-node.github.io/log4js-node/categories.html

Demonstrates category inheritance using dots (e.g., 'catA.catB'). Events in 'catA.catB' will use appenders and levels from 'catA' if not specified, and also log to 'app' appender. This is useful for hierarchical logging structures.

```javascript
const log4js = require("log4js");
log4js.configure({
  appenders: {
    console: { type: "console" },
    app: { type: "file", filename: "application.log" },
  },
  categories: {
    default: { appenders: ["console"], level: "trace" },
    catA: { appenders: ["console"], level: "error" },
    "catA.catB": { appenders: ["app"], level: "trace" },
  },
});

const loggerA = log4js.getLogger("catA");
loggerA.error("This will be written to console with log level ERROR");
loggerA.trace("This will not be written");
const loggerAB = log4js.getLogger("catA.catB");
loggerAB.error(
  "This will be written with log level ERROR to console and to a file"
);
loggerAB.trace(
  "This will be written with log level TRACE to console and to a file"
);

```

--------------------------------

### Configure Pattern Layout with Logger Context

Source: https://log4js-node.github.io/log4js-node/layouts.html

Shows how to use values from the logger's context within a pattern layout. The '%X{user}' specifier retrieves the 'user' value previously set using logger.addContext().

```javascript
log4js.configure({
  appenders: {
    out: {
      type: "stdout",
      layout: {
        type: "pattern",
        pattern: "%d %p %c %X{user} %m%n",
      },
    },
  },
  categories: { default: { appenders: ["out"], level: "info" } },
});
const logger = log4js.getLogger();
logger.addContext("user", "charlie");
logger.info("doing something.");

```

--------------------------------

### Configure MultiFile Appender by Category

Source: https://log4js-node.github.io/log4js-node/multiFile.html

Use this configuration to split logs into separate files based on the category name. Ensure the 'multi' appender is configured with 'property: "categoryName"'.

```javascript
log4js.configure({
  appenders: {
    multi: {
      type: "multiFile",
      base: "logs/",
      property: "categoryName",
      extension: ".log",
    },
  },
  categories: {
    default: { appenders: ["multi"], level: "debug" },
  },
});

const logger = log4js.getLogger();
logger.debug("I will be logged in logs/default.log");
const otherLogger = log4js.getLogger("cheese");
otherLogger.info("Cheese is cheddar - this will be logged in logs/cheese.log");

```

--------------------------------

### Basic Usage of log4js-node

Source: https://log4js-node.github.io/log4js-node/index.html

Initialize a logger and set its level for basic logging. The default log level is OFF.

```javascript
var log4js = require("log4js");
var logger = log4js.getLogger();
logger.level = "debug"; // default level is OFF - which means no logs at all.
logger.debug("Some debug messages");

```

--------------------------------

### Configure and Use Recording Appender

Source: https://log4js-node.github.io/log4js-node/recording.html

Configure log4js to use the 'recording' appender for in-memory log storage, useful for testing. This snippet demonstrates basic logging and retrieving/clearing recorded events.

```javascript
const recording = require("log4js/lib/appenders/recording");
const log4js = require("log4js");
log4js.configure({
  appenders: { vcr: { type: "recording" } },
  categories: { default: { appenders: ["vcr"], level: "info" } },
});

const logger = log4js.getLogger();
logger.info("some log event");

const events = recording.replay(); // events is an array of LogEvent objects.
recording.erase(); // clear the appender's array.

```

--------------------------------

### Configure Pattern Layout with Custom Token

Source: https://log4js-node.github.io/log4js-node/layouts.html

Demonstrates how to define and use a custom token within a pattern layout. The custom token 'user' is defined as a function that retrieves the current user, and it's included in the log pattern.

```javascript
log4js.configure({
  appenders: {
    out: {
      type: "stdout",
      layout: {
        type: "pattern",
        pattern: "%d %p %c %x{user} %m%n",
        tokens: {
          user: function (logEvent) {
            return AuthLibrary.currentUser();
          },
        },
      },
    },
  },
  categories: { default: { appenders: ["out"], level: "info" } },
});
const logger = log4js.getLogger();
logger.info("doing something.");

```

--------------------------------

### Configure Basic File Appender

Source: https://log4js-node.github.io/log4js-node/file.html

Configure the file appender to write all logs to a single file. Ensure to call log4js.shutdown on application termination.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});

const logger = log4js.getLogger();
logger.debug("I will be logged in all-the-logs.log");

```

--------------------------------

### Configure TCP Server Appender

Source: https://log4js-node.github.io/log4js-node/tcp-server.html

Configure the TCP server appender to listen on a specific host and forward logs to a file appender. Ensure the server appender is not listed in categories to avoid self-logging.

```javascript
log4js.configure({
  appenders: {
    file: { type: "file", filename: "all-the-logs.log" },
    server: { type: "tcp-server", host: "0.0.0.0" },
  },
  categories: {
    default: { appenders: ["file"], level: "info" },
  },
});

```

--------------------------------

### Configure stdout appender with messagePassThrough layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

Sets up the stdout appender to use the messagePassThrough layout. This layout is useful for appenders that serialize events in a specific format, as it only outputs the log event data.

```javascript
log4js.configure({
  appenders: {
    out: { type: "stdout", layout: { type: "messagePassThrough" } },
  },
  categories: { default: { appenders: ["out"], level: "info" } },
});
```

--------------------------------

### Logger Management - log4js.getLogger([category])

Source: https://log4js-node.github.io/log4js-node/api.html

Retrieves a logger instance. If log4js is not configured, it will be configured with default settings. You can specify a category for the logger or use the default category.

```APIDOC
## Logger Management - `log4js.getLogger([category])`

### Description
Retrieves a logger instance. If log4js is not configured, it will be configured with default settings. You can specify a category for the logger or use the default category.

### Method
`log4js.getLogger([category])`

### Parameters
#### Path Parameters
- **category** (string) - Optional - The category name for the logger. Defaults to 'default' if not provided.

### Logger Object Methods

#### `<level>(args...)`
- **Description**: Dispatches a log event with the specified level. The level can be any lowercase name of the defined log levels (e.g., 'info', 'warn', 'error'). Formatting placeholders like `%s` and `%d` are delegated to `util.format`.
- **Example**: `logger.info('User logged in: %s', userId)`

#### `is<level>Enabled()`
- **Description**: Returns `true` if a log event of the specified level (camel case, e.g., `isInfoEnabled`) would be dispatched. This depends on the logger's configured level.
- **Example**: `if (logger.isInfoEnabled()) { logger.info('This is an informational message.'); }`

#### `addContext(key, value)`
- **Description**: Adds a key-value pair to the logger's context. This context is added to all log events generated by this logger. Primarily used by `logFaces` appenders for tracking information like user IDs.
- **Parameters**:
  - **key** (string) - Required - The key for the context data.
  - **value** (any) - Required - The value to associate with the key.
- **Example**: `logger.addContext('userId', 'abc-123')`

#### `removeContext(key)`
- **Description**: Removes a previously defined key-value pair from the logger's context.
- **Parameters**:
  - **key** (string) - Required - The key of the context data to remove.
- **Example**: `logger.removeContext('userId')`

#### `clearContext()`
- **Description**: Removes all context key-value pairs from the logger.
- **Example**: `logger.clearContext()`

#### `setParseCallStackFunction(function | undefined)`
- **Description**: Allows overriding the default function used to parse call stack data for log layouts. A generic JavaScript `Error` object is passed to this function. It must return an object with properties like `fileName`, `lineNumber`, `columnNumber`, `callStack`, `className`, `functionName`, `functionAlias`, and `callerName`. Passing `undefined` resets it to the default parser.
- **Parameters**:
  - **function** (function | undefined) - Optional - The custom function to parse the call stack, or `undefined` to reset to default.
- **Example**: `logger.setParseCallStackFunction(myCustomParser)`

### Logger Object Properties

#### `level`
- **Description**: Overrides the configured log level for this logger. Can be a log4js level object or a string (e.g., 'info', 'INFO'). Changing this affects all loggers of the same category.
- **Type**: `string` or `object`

#### `useCallStack`
- **Description**: Overrides the configured `useCallStack` setting for this logger. If `true`, log events will include call stack information (line numbers, file names). Changing this affects all loggers of the same category.
- **Type**: `boolean`

#### `callStackLinesToSkip`
- **Description**: Customizes how many lines of the call stack are skipped when parsing. Defaults to `0`. Useful for ignoring wrapper functions in the stack trace.
- **Type**: `number`
```

--------------------------------

### Replicating Console Logging in v2

Source: https://log4js-node.github.io/log4js-node/migration-guide.html

This code snippet shows how to replicate the v1 behavior of replacing node.js console functions with log4js loggers in v2. Ensure log4js is configured before binding console methods.

```javascript
log4js.configure(...); // set up your categories and appenders
const logger = log4js.getLogger('console'); // any category will work
console.log = logger.info.bind(logger); // do the same for others - console.debug, etc.
```

--------------------------------

### Configure stdout appender with dummy layout

Source: https://log4js-node.github.io/log4js-node/layouts.html

Configures the stdout appender to use the dummy layout. This layout is primarily intended for specific appenders like logstashUDP and outputs only the first value in the log event's data.

```javascript
log4js.configure({
  appenders: { out: { type: "stdout", layout: { type: "dummy" } } },
  categories: { default: { appenders: ["out"], level: "info" } },
});
```

--------------------------------

### Configure log4js for PM2 with Custom Instance Variable

Source: https://log4js-node.github.io/log4js-node/clustering.html

Configure log4js to work with PM2 by setting `pm2: true`. If you use a custom environment variable for PM2 instances (e.g., 'INSTANCE_ID'), specify it using `pm2InstanceVar`.

```javascript
log4js.configure({
  appenders: { out: { type: "stdout" } },
  categories: { default: { appenders: ["out"], level: "info" } },
  pm2: true,
  pm2InstanceVar: "INSTANCE_ID",
});

```

--------------------------------

### Configure Status Code Rulesets

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Customize the log levels for specific HTTP status code ranges using the statusRules option in connectLogger.

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    statusRules: [
      { from: 200, to: 299, level: "debug" },
      { codes: [303, 304], level: "info" },
    ],
  })
);

```

--------------------------------

### Configure custom appender module

Source: https://log4js-node.github.io/log4js-node/appenders.html

Load a custom appender module named 'gouda' with a specific flavor. This demonstrates using external appender modules.

```javascript
log4js.configure({
  appenders: { gouda: { type: "cheese/appender", flavour: "tasty" } },
  categories: { default: { appenders: ["gouda"], level: "debug" } },
});

```

--------------------------------

### log4js.isConfigured()

Source: https://log4js-node.github.io/log4js-node/api.html

Checks if the log4js library has been configured. This includes explicit calls to `configure` or implicit configuration via `getLogger`.

```APIDOC
## GET /log4js.isConfigured

### Description
Checks if the log4js library has been initialized via `configure()`.

### Method
GET

### Endpoint
/log4js.isConfigured

### Parameters
None

### Request Example
```json
{}
```

### Response
#### Success Response (200)
- **configured** (boolean) - True if log4js has been configured, false otherwise.

#### Response Example
```json
{
  "configured": true
}
```
```

--------------------------------

### Configure Default Daily Log Rolling

Source: https://log4js-node.github.io/log4js-node/dateFile.html

Use this configuration for daily log file rotation. The log file will be named based on the current date.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "dateFile", filename: "all-the-logs.log" },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
  },
});
```

--------------------------------

### Configure appender by passing module object

Source: https://log4js-node.github.io/log4js-node/appenders.html

Pass a custom appender module object directly into the configuration. Useful for bundlers like webpack.

```javascript
const myAppenderModule = {
  configure: (config, layouts, findAppender, levels) => {
    /* ...your appender config... */
  },
};
log4js.configure({
  appenders: { custom: { type: myAppenderModule } },
  categories: { default: { appenders: ["custom"], level: "debug" } },
});

```

--------------------------------

### Custom Layout Using Response Context

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Define a custom log layout that utilizes the response object from the logging event context to include status information in logs.

```javascript
log4js.addLayout("customLayout", () => {
  return (loggingEvent) => {
    const res = loggingEvent.context.res;
    return util.format(
      ...loggingEvent.data,
      res ? `status: ${res.statusCode}` : ""
    );
  };
});

```

--------------------------------

### Custom Log Format with Express Logger

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Configure the connectLogger with a custom format string or a formatting function for detailed log messages. Supports Express 3.x and 4.x.

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: log4js.levels.INFO,
    format: ":method :url",
  })
);

```

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    // include the Express request ID in the logs
    format: (req, res, format) =>
      format(
        `:remote-addr - ${req.id} - ":method :url HTTP/:http-version" :status :content-length ":referrer" ":user-agent"`
      ),
  })
);

```

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: "info",
    format: (req, res, format) =>
      format(`:remote-addr :method :url ${JSON.stringify(req.body)}`),
  })
);

```

--------------------------------

### Automatic Log Level Detection

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Enable automatic log level detection for connect-logger based on HTTP status codes. Compatible with Express 3.x and 4.x.

```javascript
app.use(log4js.connectLogger(logger, { level: "auto" }));

```

--------------------------------

### Configure Standard Output Appender

Source: https://log4js-node.github.io/log4js-node/stdout.html

Configures the stdout appender for log4js. This is the default appender and writes logs to the standard output stream. Ensure the appender type is set to 'stdout'.

```javascript
log4js.configure({
  appenders: { out: { type: "stdout" } },
  categories: { default: { appenders: ["out"], level: "info" } },
});

```

--------------------------------

### Configure Call Stack Usage

Source: https://log4js-node.github.io/log4js-node/api.html

Allows overriding the 'useCallStack' configuration for a logger category. This affects line number and file name generation in log events.

```javascript
logger.useCallStack = true;
```

--------------------------------

### Custom Layouts - log4js.addLayout(type, fn)

Source: https://log4js-node.github.io/log4js-node/api.html

Allows you to define and register custom log layout functions. These functions format log events according to your specific needs.

```APIDOC
## Custom Layouts - `log4js.addLayout(type, fn)`

### Description
This function is used to add user-defined layout functions to log4js. These custom layouts can then be used in your log4js configuration.

### Method
`log4js.addLayout(type, fn)`

### Parameters
#### Path Parameters
- **type** (string) - Required - The name of the layout type (e.g., 'myCustomLayout').
- **fn** (function) - Required - The layout function. This function receives the log event data and should return a formatted string.

### Request Example
```javascript
log4js.addLayout('json', (logEvent) => {
  return JSON.stringify({
    timestamp: logEvent.startTime,
    level: logEvent.level.levelStr,
    message: logEvent.messages.join(' '),
    category: logEvent.categoryName
  });
});

// Then in your log4js configuration:
// {
//   type: 'console',
//   layout: { type: 'json' }
// }
```
```

--------------------------------

### Replace console logging with log4js

Source: https://log4js-node.github.io/log4js-node/faq.html

Manually override console methods like `console.log` to use a specific log4js logger. This requires configuring log4js first and then binding the logger methods to the console functions.

```javascript
log4js.configure(...); // set up your categories and appenders
const logger = log4js.getLogger('console');
console.log = logger.info.bind(logger); // do the same for others - console.debug, etc.

```

--------------------------------

### Configure TCP Appender

Source: https://log4js-node.github.io/log4js-node/tcp.html

Configure the TCP appender to send error messages to a remote log server. Ensure the log server is running and configured to receive logs.

```javascript
log4js.configure({
  appenders: {
    network: { type: "tcp", host: "log.server" },
  },
  categories: {
    default: { appenders: ["network"], level: "error" },
  },
});

```

--------------------------------

### Add Custom Layout

Source: https://log4js-node.github.io/log4js-node/api.html

Registers a user-defined layout function with log4js. This allows for custom log message formatting.

```javascript
log4js.addLayout('myLayout', function(config) {
  return function(loggingEvent) {
    // custom layout logic
    return `${loggingEvent.startTime} - ${loggingEvent.level.levelStr} - ${loggingEvent.data.join(' ')}`;
  };
});
```

--------------------------------

### Configure Multiprocess Appender as Master

Source: https://log4js-node.github.io/log4js-node/multiprocess.html

Configure the multiprocess appender in master mode to listen for log events from workers. The `appender` property specifies where the master should send received logs.

```javascript
log4js.configure({
  appenders: {
    file: { type: "file", filename: "all-the-logs.log" },
    server: {
      type: "multiprocess",
      mode: "master",
      appender: "file",
      loggerHost: "0.0.0.0",
    },
  },
  categories: {
    default: { appenders: ["file"], level: "info" },
  },
});
```

--------------------------------

### Add Context to Logger

Source: https://log4js-node.github.io/log4js-node/api.html

Adds a key-value pair to all log events generated by this logger. Useful for tracking requests or user sessions.

```javascript
logger.addContext('requestId', 'abc-123');
```

--------------------------------

### Log Message with Level

Source: https://log4js-node.github.io/log4js-node/api.html

Dispatches a log event with a specific level. Supports util.format placeholders for string formatting.

```javascript
logger.info('User %s logged in from %s', user.name, user.ip);
```

--------------------------------

### Configure Call Stack Lines to Skip

Source: https://log4js-node.github.io/log4js-node/api.html

Customizes the number of call stack lines to skip when parsing error stacks. Useful for ignoring wrapper functions.

```javascript
logger.callStackLinesToSkip = 1;
```

--------------------------------

### Enable line numbers in log output

Source: https://log4js-node.github.io/log4js-node/faq.html

Configure log4js to include line numbers in log messages by enabling `enableCallStack` for the category and using a pattern layout that includes `%f` (file) and `%l` (line number).

```javascript
const log4js = require("log4js");
log4js.configure({
  appenders: {
    out: {
      type: "stdout",
      layout: {
        type: "pattern",
        pattern: "%d %p %c %f:%l %m%n",
      },
    },
  },
  categories: {
    default: { appenders: ["out"], level: "info", enableCallStack: true },
  },
});
const logger = log4js.getLogger("thing");
logger.info("this should give me a line number now");

```

--------------------------------

### Shutdown - log4js.shutdown([callback])

Source: https://log4js-node.github.io/log4js-node/api.html

Gracefully shuts down log4js by closing all appenders and ensuring all pending log events are written. This should be called before your application exits.

```APIDOC
## Shutdown - `log4js.shutdown([callback])`

### Description
Gracefully shuts down log4js by closing all appenders and ensuring all pending log events are written. This should be called before your application exits to guarantee all logs are flushed and resources are released.

### Method
`log4js.shutdown([callback])`

### Parameters
#### Path Parameters
- **callback** (function) - Optional - A function to be called once log4js has finished shutting down.

### Response Example
```javascript
log4js.shutdown(() => {
  console.log('Log4js has shut down successfully.');
});
```
```

--------------------------------

### Configure Console Appender in log4js-node

Source: https://log4js-node.github.io/log4js-node/console.html

Configure the console appender for log4js-node. Ensure the appender type is set to 'console' and specify the default category level.

```javascript
log4js.configure({
  appenders: { console: { type: "console" } },
  categories: { default: { appenders: ["console"], level: "info" } },
});

```

--------------------------------

### Exclude Logs with Nolog Option

Source: https://log4js-node.github.io/log4js-node/connect-logger.html

Use the nolog option to specify patterns (string, regexp, array, or function) to omit certain log messages from being recorded.

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    format: ":method :url",
    nolog: ".gif|\.jpg$",
  })
);

```

```javascript
app.use(
  log4js.connectLogger(logger, {
    level: "auto",
    format: ":method :url",
    nolog: (req, res) => res.statusCode < 400,
  })
);

```

--------------------------------

### Handle Memory Usage with 'log4js:pause' Events

Source: https://log4js-node.github.io/log4js-node/dateFile.html

Listen for 'log4js:pause' events to manage memory usage when the appender is buffering messages. Stop logging when `true` is received and resume when `false` is received.

```javascript
log4js.configure({
  appenders: {
    output: { type: "dateFile", filename: "out.log" },
  },
  categories: { default: { appenders: ["output"], level: "debug" } },
});

let paused = false;
process.on("log4js:pause", (value) => (paused = value));

const logger = log4js.getLogger();
while (!paused) {
  logger.info("I'm logging, but I will stop once we start buffering");
}
```

--------------------------------

### Configure Appenders Without Category Filter

Source: https://log4js-node.github.io/log4js-node/categoryFilter.html

This configuration achieves a similar outcome to the category filter by setting the log level of the 'noisy.component' category to 'off', effectively preventing its logs from being written to 'all-the-logs.log'. This method is an alternative when direct control over category logging levels is preferred.

```javascript
log4js.configure({
  appenders: {
    everything: { type: "file", filename: "all-the-logs.log" },
  },
  categories: {
    default: { appenders: ["everything"], level: "debug" },
    "noisy.component": { appenders: ["everything"], level: "off" },
  },
});

const logger = log4js.getLogger();
const noisyLogger = log4js.getLogger("noisy.component");
logger.debug("I will be logged in all-the-logs.log");
noisyLogger.debug("I will not be logged.");

```

--------------------------------

### Configure Logger Level

Source: https://log4js-node.github.io/log4js-node/api.html

Allows overriding the configured log level for a specific logger category. Changes apply to all loggers of that category.

```javascript
logger.level = 'DEBUG';
```

--------------------------------

### Check Log Level Enabled

Source: https://log4js-node.github.io/log4js-node/api.html

Returns true if a log event of the specified level would be dispatched. Useful for performance optimizations.

```javascript
if (logger.isInfoEnabled()) {
  logger.info('This will only be logged if INFO level is enabled');
}
```

--------------------------------

### Set Custom Call Stack Parser

Source: https://log4js-node.github.io/log4js-node/api.html

Allows overriding the default call stack parsing logic. The provided function must return specific properties about the call stack.

```javascript
logger.setParseCallStackFunction(function (error) {
  // custom parsing logic
  return {
    fileName: error.fileName,
    lineNumber: error.lineNumber,
    columnNumber: error.columnNumber,
    callStack: error.callStack,
    className: error.className,
    functionName: error.functionName,
    functionAlias: error.functionAlias,
    callerName: error.callerName
  };
});
```

```javascript
logger.setParseCallStackFunction(undefined); // Reset to default
```

--------------------------------

### Configure Standard Error Appender

Source: https://log4js-node.github.io/log4js-node/stderr.html

Configures log4js to use the standard error appender. This appender writes all log events to the standard error stream. Ensure the appender type is set to 'stderr'.

```javascript
log4js.configure({
  appenders: { err: { type: "stderr" } },
  categories: { default: { appenders: ["err"], level: "ERROR" } },
});

```