findFiles-extended.js

'use strict'

// Dependencies
const EventEmitter = require('events').EventEmitter
const path = require('path')

// Definition
class FindFiles extends EventEmitter {

  constructor (extension) {
    super()
    this.extension = extension
    this.files = []
  }

  addFile (file) {
    this.files.push(file)
    return this
  }

  // Check for matches
  findFiles () {
    process.nextTick(() => {
      this.files.forEach(file => {
        if (path.extname(file) === this.extension) {
          this.emit('match', file)
        }
      })
    })
    return this
  }
}

// Instantiation of observable object
const FindFilesSearcher = new FindFiles('.js')

// Implementation
FindFilesSearcher
  .addFile('file1.js')
  .addFile('file2.md')
  .addFile('file3.js')
  .findFiles()
  .on('match', console.log)
  .on('error', err => {
    return console.error(err)
  })