register-listeners

register multiple event listeners at once for nodeJS.

intro

Originally Updated on 25 - 01 - 2021

Normally, when you want to add multiple event listeners in JavaScript, you would do it like this:

// say for example you're using MongooseJS
const connection = Mongoose.connection
connection.on("connecting", () => log.info('connecting to Database...'))
connection.on("reconnected", () => log.success('connection to database has been Re-Established successfully'))
connection.on("disconnected", () => log.warn('disconnected from database'))
connection.on("error", (error) => log.error(error.message))
// connection.on("connected", () => log.success('DB connection established'))

Using register-listeners:

registerListener(Mongoose.connection, {
    connecting: () => log.info('connecting to Database...'),
    reconnected: () => log.success('connection to database has been Re-Established successfully'),
    disconnected: () => log.warn('disconnected from database'),
    error: (error) => log.error(error.message),
    // connected: () => log.success('DB connection established'),
})

Using register-listeners is a lot cleaner if you're registering more and more event listeners.

register-listeners helps you adding async callbacks too, which is very cool.

Side note about the log() function

throughout this guide, I'll be using the log() functions from @samislam/log, it's a simple module that helps you to print colorful output to your console, which makes the development and debugging process a lot easier. you can install it from npm.

Usage

registerListeners(on, obj)

argument	Description
on
obj

Code sample

The following is optional to read, it's just to give you an idea of how an application could be structured using register-listeners.

in this code sample, I was creating a function that uses expressJS, it adds a service on port 3000 for serving HTTP requests. the purpose was to test register-listeners.

It was easier to use register-listeners to complete this job, all the code required for this one job is done in one code block, this code block is stored in an independant module called app.js.

all the processes of error handling (simple error handling to fit my case at that time) is done inside this single code block using register-listeners.

const listen = (port) => {
  return new Promise((resolve, reject) => {
    const server = app.listen(port)
    registerListener(server, {
      // * for more events, see https://nodejs.org/api/net.html#net_class_net_server
      listening() {
        const message = `Listening on port ${port}...`
        log.info(message)
        resolve(server)
      },
      error: {
        async callback(error) {
          if (error.code === 'EADDRINUSE') {
            this.times = this.times - 1
            let message
            if (this.showErrMsg) {
              message = tc(`port ${port} is already in use`)
              log.error(message)
              this.showErrMsg = false
            }
            message = `trying to restart the service on port ${port}... attempts left ${this.times}`
            log.warn(message)
            // server.close()
            if (this.times !== 0) {
              setTimeout(() => server.listen(port), this.duration)
            } else {
              // prettier-ignore
              const error = new Error(tc(`port ${port} is already being used by another service, unable to start express app for service test`))
              reject(error)
            }
          }
        },
        properties: {
          times: 5,
          duration: 5000,
          showErrMsg: true,
        },
      },
    })
  })
}

this documentation is not complete.