Why does the vowel function not return the right value?

Question

I’m trying to do a function that reads a txt file and returns the number of vowels in the file.

const fs = require('fs');
let texto = "Teste";//tem 2 vogais
fs.writeFile("teste.txt",texto ,(err)=>{
    if(err) {
        throw err;
    }

    console.log("Arquivo salvo");
});

function vogal (file) {
    const letras = ["a", "e", "i", "o", "u"];
    var cont = 1;    
    fs.readFile(file, (err, data) =>{
        if(err) throw err;

        data.toString().split("").forEach(itemTexto =>{
            letras.forEach(itemLetra=>{
                if(itemTexto === itemLetra) cont++;
            });
        });

    });
    return cont;//retorna 1
}

console.log(vogal("teste.txt"));

Answer 1

You are returning the value of cont before you finish reading your file. As you may already know, Javascript input and output operations are asynchronous, which means that the callback in which you count the characters in your file is the last thing running in your function.

If you want to return the value of an asynchronous process, you have to return within a Promise, or do the console.log within the function itself:

const fs = require('fs')
const util = require('util')

async function consoante(file) {
    // Não me responsabilizo por letras como H, W e Y
    var consoantes = new Set('bBcCdDfFgGjJkKlLmMnNpPqQrRsStTvVwWxXzZ')
    var cont = 0

    var readFile = util.promisify(fs.readFile)
    var buffer = await readFile(file)

    var str = buffer.toString().normalize('NFD')
    for (var c of str)
        if (consoantes.has(c)) cont++

    console.log(`Número de consoantes: ${cont}`)
}