electronjs app async/await not waiting return data from function

Question

I am new to Electron nodejs app. I make a call from html to main.js using ipcRenderer.on call. The code in main.js follows below, where i read an array of folders, fetch files from each folder and read contents from each file to process further. Now the problem is that the main function does not wait for the content read function to return the data.

ipcMain.on('worker', async (event, arg) => {
    for (let x = 0; x < folders.length; x++) {
        event.reply("dex-worker", dexFolders[x].path);
        // Scan folders for files
        fs.readdir(folders[x].path, (err, files) => {
            // Process files
            files.forEach(async (file) => {
            event.reply("worker", file.toString()); // THIS WORKS
            var fdata = await readData(files[x].path + path.sep + file); // DOES NOT WAIT for RETURN
            console.log(fdata); // displays 'undefined'});
        });
    }
});

async function readData(fi) {
    var _fdata = "";
    fs.readFile(fi, 'utf8', function (err, data) {
        if (err) {
            console.log(err);
        }
        _fdata = data;
        return (_fdata);
    });
}

I read many post and docs regarding async/await and promise. But i do not understand whether they are together or alternatives. Please help.

Prime · Accepted Answer · 2020-12-26 08:19:49Z

3

You can use callback to get data properly.

ipcMain.on('worker', async (event, arg) => {
  for (let x = 0; x < folders.length; x++) {
    event.reply("dex-worker", dexFolders[x].path);
    // Scan folders for files
    fs.readdir(folders[x].path, (err, files) => {
      // Process files
      files.forEach(async (file) => {
        event.reply("worker", file.toString()); // THIS WORKS
        readData(files[x].path + path.sep + file, (err, data) => {
          if (err) {
            console.log(err);
          }
          console.log(data);
        });
      });
    })
  }
});

function readData(fi, callback) {
  fs.readFile(fi, 'utf8', callback);
}

answered Dec 26, 2020 at 8:19

Prime

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