How to get a variable that is nested inside another function

Question

So, I have this code:

function readLineMemory() {
loadFile = dialog.showOpenDialog({properties: ['openFile']});
console.log(loadFile);
var lr = new LineByLineReader(loadFile[0]);
lr.on('error', err => {
    return console.log(err);
});
lr.on('line', function (line) { // called every line
    // var html = '';
    const lineParse = JSON.parse(line);
    JSONParsed.push(lineParse);
    let htmlTabled = tableify(lineParse) + '<hr>';
    html = html + htmlTabled;
});
lr.on('end', function () { // called when file is read fully
    html = 'data:text/html,' + html;
})} return html

However, when I try to return the html value, it just returns undefined. I have been banging my head on the wall for a while with this, and I just cannot figure out what I am doing wrong. As far as I'm aware, the code isn't async. The html value should actually be a string of html code that I am using in another function.

1. to answer the direct question, you can't 2. to answer your specific problem - the functions there are asynchronous, hence you can't return the value that gets populated later. — VLAZ, Sep 25 '16 at 01:15
declare a global. assign the value of html to your global in your `.on("end")`. Get rid of the `return html`. Delete this question. Read the dozens of other questions exactly like it — Tibrogargan, Sep 25 '16 at 01:18

Jacob · Accepted Answer · 2016-09-25T01:26:30.257

The callbacks are asynchronous, according to what I see in the code here: https://github.com/Osterjour/line-by-line/blob/master/line-by-line.js#L43-L45

setImmediate(function () {
    self._initStream();
});

The parsing doesn't start until the next "tick" in the event loop. Generally, it's good to assume that most callbacks take place asynchronously. You'll want to convert your function to also be asynchronous:

function readLineMemory(cb) {
  let html = '';
  const loadFile = dialog.showOpenDialog({properties: ['openFile']});
  const lr = new LineByLineReader(loadFile[0]);
  lr.on('error', err => {
      cb(err);
    })
    .on('line', function (line) { // called every line
      const lineParse = JSON.parse(line);
      JSONParsed.push(lineParse);
      let htmlTabled = tableify(lineParse) + '<hr>';
      html = html + htmlTabled;
    })
    .on('end', function () { // called when file is read fully
      html = 'data:text/html,' + html;
      cb(null, html);
    });
}

(or IMO even better with promises):

function readLineMemory() {
  return new Promise(function (resolve, reject) {
    let html = '';
    const loadFile = dialog.showOpenDialog({properties: ['openFile']});
    const lr = new LineByLineReader(loadFile[0]);
    lr.on('error', err => {
        reject(err);
      })
      .on('line', function (line) { // called every line
        const lineParse = JSON.parse(line);
        JSONParsed.push(lineParse);
        let htmlTabled = tableify(lineParse) + '<hr>';
        html = html + htmlTabled;
      })
      .on('end', function () { // called when file is read fully
        html = 'data:text/html,' + html;
        resolve(html);
      });
  });
}

This has infact solved my problem! Will accept when it lets me. — willyb321, Sep 25 '16 at 01:22

How to get a variable that is nested inside another function

1 Answers1