How to save the data from a txt file returns to an array that is outside the function?

Question

It's my first time using javascript and I'm trying to do is save the data extracted from a .txt file in an array that I've declared outside and at the beginning of the code. (It's Electron framework).

I tried to extract the data and to save into the array.

const { remote } = require('electron')
const app = remote.app
const $ = require('jquery')
const fs = require('fs')
const dialog = remote.dialog

const win = remote.getCurrentWindow()

let dataMeetingsFromTxt

{...}

function readMeetingsToSaveIntoArray() {
  dataMeetingsFromTxt = []
  fs.readFile('./dataMeetings.txt', 'utf-8', (err, data) => {
    if (err) throw err;
    dataMeetingsFromTxt = data.toString().split("\n");
  })
}

{...}

$('.oneBTN').on('click', () => {
  readMeetingsToSaveIntoArray()
  console.log(dataMeetingsFromTxt.length) //The output is always 'undefined'
})

The output is always 'undefined'.

Answer 1

This is because fs.readFile is asynchronous. The 3rd args is a call back and this is where the console.log should be done. Else the console.log on your click handler will be executed before the readFile's callback.

const { remote } = require('electron')
const app = remote.app
const $ = require('jquery')
const fs = require('fs')
const dialog = remote.dialog

const win = remote.getCurrentWindow()

let dataMeetingsFromTxt

{...}

function readMeetingsToSaveIntoArray() {
  dataMeetingsFromTxt = []
  fs.readFile('./dataMeetings.txt', 'utf-8', (err, data) => {
    if (err) throw err;
    dataMeetingsFromTxt = data.toString().split("\n");
    console.log(dataMeetingsFromTxt.length);
  })
}

{...}

$('.oneBTN').on('click', () => {
  readMeetingsToSaveIntoArray()
})