When the type is module, there is an error when reading Appenders. How to deal with it

[artiely]

package.json

+"type":"module",

node v16.15.0
log4js ^6.4.5

import log4js from "log4js"
log4js.configure({
  appenders: {
    tiktok: {
      type: 'log'
    },
    everything: {
      type: 'file',
      filename: 'all-the-logs.log'
    },
    emergencies: { type: 'file', filename: 'errors.log' },
    justError: {
      type: 'logLevelFilter',
      appender: 'emergencies',
      level: 'error'
    }
  },
  categories: { default: { appenders: ['tiktok', 'everything', 'justError'], level: 'debug' } },
  pm2: true,
  pm2InstanceVar: 'NODE_APP_INSTANCE',
})

log.js

function stdoutAppender(layout, timezoneOffset) {
  const appender = (loggingEvent) => {
    if (loggingEvent.level.levelStr == "DEBUG") {
      process.stdout.write(`${layout(loggingEvent, timezoneOffset)}\n`);
    } else if (loggingEvent.level.levelStr == "INFO") {
     //
      process.stdout.write(`${layout(loggingEvent, timezoneOffset)}\n`);
    };
  }

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

  return appender;
}

// 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

tanjie@tanjiedeMacBook-Pro back % node index.js
/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/configuration.js:31
      throw new Error(`Problem with log4js configuration: (${util.inspect(config, { depth: 5 })})`
            ^

Error: Problem with log4js configuration: ({
  appenders: {
    tiktok: { type: 'log' },
    everything: { type: 'file', filename: 'all-the-logs.log' },
    emergencies: { type: 'file', filename: 'errors.log' },
    justError: { type: 'logLevelFilter', appender: 'emergencies', level: 'error' }
  },
  categories: {
    default: {
      appenders: [ 'tiktok', 'everything', 'justError' ],
      level: 'debug'
    }
  },
  pm2: true,
  pm2InstanceVar: 'NODE_APP_INSTANCE'
}) - appender "/Users/tanjie/Desktop/danmu-plus/back/log" could not be loaded (error was: Error [ERR_REQUIRE_ESM]: require() of ES Module /Users/tanjie/Desktop/danmu-plus/back/log.js from /Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js not supported.
Instead change the require of log.js in /Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js to a dynamic import() which is available in all CommonJS modules.)
    at /Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/configuration.js:31:13
    at Array.forEach (<anonymous>)
    at Object.throwExceptionIf (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/configuration.js:29:9)
    at tryLoading (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:31:19)
    at loadAppenderModule (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:44:6)
    at createAppender (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:65:29)
    at getAppender (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:56:20)
    at /Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:117:7
    at Array.forEach (<anonymous>)
    at setup (/Users/tanjie/Desktop/danmu-plus/back/node_modules/log4js/lib/appenders/index.js:112:33)
tanjie@tanjiedeMacBook-Pro back % 

[lamweili]

While your project is in ESM, log4js is in CJS.
Thus, when log4js (CJS) attempts to require your custom appender log.js (ESM), it will not work.

---

There are two ways:

1. Your log.js custom appender can be explicitly declared as a CJS.
   With PR fix: load CJS appenders for ESM packages #1280, rename log.js to log.cjs. That should work.

2. Alternatively, you can also take a look at
   Custom appender support for ESM project #1122 (comment) by importing the appender yourself and then passing it to log4js.configure().

[lamweili]

@artiely Did you managed to get this resolved?