Using values from an excel file in JS

am ne in JS
I have several questions:

The code below, it is opening/extracting the information from XLS properly
I would like:

1. How can I make that I should be able to access results after having finised *readXlsxFile * procedure?
2. I would like to make the computer to wait 1 second after consoling each line.
   I was not able to get it to work
3. One of my attempts was readXlsx().then(()=>{}) but it also gave me an error. Why?

const readXlsxFile = require("read-excel-file/node");
const fs = require('fs')
// const results = [];
var results = [];
let maxRow

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

function readXlsx() {
  
  readXlsxFile('./myfile.xlsx')
    .then((rows) => {
      console.log("Wait!!")
      results.push(rows)    // Push the complete result into array

      // console.log(results)

      var maxRow = rows.length
      // nRow = 0 Will be the title. WILL NOT CONSOLE
      for (var nRow  = 1; nRow<maxRow-1; nRow++) {
        if (nRow <= 10) {
          console.log(nRow)
          console.log(results[0][nRow][0])
          console.log(results[0][nRow][1])
          console.log(results[0][nRow][2])
          console.log('---')
        }
        // .then(()=>{sleep(500)})      
      }

      return Promise.resolve("Success")
  })

}

function testSleep() {
    console.log("Hello");
      sleep(2000).then(() => { console.log("World!"); });
  
  // console.log(results)
  }


readXlsx()

TIA

A fundamental concept in modern JavaScript is something called a promise, which you can read more about here. This background is important for you to understand the answers to your questions.

1. There are two ways of doing this, using .then() (like you are), or using await. I find await easier to understand when thinking about promises (and it fits a bit better into the structure of what you're doing), and you can read about it here. Below is the same code, using await and async instead:

const readXlsxFile = require("read-excel-file/node");
const fs = require('fs')
// const results = [];
var results = [];
let maxRow

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

// V - Notice that this is an "async" function
async function readXlsx() {
  const rows = await readXlsxFile('./myfile.xlsx')
  results.push(rows)

  const maxRow = rows.length

  for (var nRow = 1; nRow < maxRow - 1; nRow++) {
    console.log(nRow)
    console.log()
    console.log(results[0][nRow][1])
    console.log(results[0][nRow][2])
    console.log('---')
  }
}

because we are now awaiting the result of the readXlsxFile function, the code will not continue before readXlsxFile is finished. This way, if you refer to the function in another area, results will be properly defined:

// ... this is a continuation of your code
async function logMyResults() {
  await readXlsx()

  // This will not run until readXlsx() is done, since it's being `await`ed
  console.log(results)
}

while you should probably just be returning results instead, that is how it would work in the way you currently have everything set up.

2. I think you were misunderstanding how .then() works. .then() is how you would run code after a promise finishes. The problem is that only the code within the function you provide to .then() will be run after the promise is done, and everything else outside of it will continue running without waiting. Using the same async/await code above, you can now use sleep as intended:

async function readXlsx() {
  const rows = await readXlsxFile('./myfile.xlsx')
  results.push(rows)

  const maxRow = rows.length

  for (var nRow = 1; nRow < maxRow - 1; nRow++) {
    console.log(nRow)
    console.log()
    console.log(results[0][nRow][1])
    console.log(results[0][nRow][2])
    console.log('---')
    
    await sleep(1000)
  }
}

which properly blocks execution within the entire function.

3. I don't know what error you got, so I have no way of knowing, but it is probably because, at that time, readXlsx was not an async function, and you can only call .then() on the results of an async function (AKA: a promise)