No output file even though variables are not empty

Question

Even though I can clearly see my output in console. I can't write them into a file. There is 1 output file and its undefined-03-02-2017.txt which contains single line '15:33 undefined'.

for (i = 0; i < channelcount; i++) {
    messages[i] -= messagesOld[i];
    console.log(channels[i] + ' ' + messages[i]);
    messages[i] = messagesOld[i];

    fs.open('logs/' + channels[i] + '.txt', 'r', function (err, fd) {
        if (err && err.code == 'ENOENT') {
            fs.writeFile('logs/' + channels[i] + '-' + moment().format('MM-DD-YYYY') + '.txt', moment().format('H:mm') + ' ' + messages[i], function (err) { });
        } else {
            fs.appendFile('logs/' + channels[i] + '-' + moment().format('MM-DD-YYYY') + '.txt', moment().format('H:mm') + ' ' + messages[i] + '\n', function () { });
        }
    });
}

Why does your channels[i] return undefined? Or was the file undefined-03-02-2017.txt not made by this function? PS: for the record, appendFIle will also create a file if it doesn't exist, so your if statement is redundant. — Shilly, Mar 02 '17 at 13:48
Thats what I can not understand. I can see them in console as output. — Pyro, Mar 02 '17 at 13:49

score 0 · Answer 1 · answered Mar 02 '17 at 13:53

0

@Pyro, you used writeFile incorrectly. Please see syntax writeFile(file, data[, options], callback)

you have to use like this

fs.writeFile('logs/' + channels[i] + '-' + moment().format('MM-DD-YYYY') + moment().format('H:mm') + '.txt ' , messages[i], function (err) { });

answered Mar 02 '17 at 13:53

Anoop Yaseen P T

81
5

What did you change to the syntax? – Shilly Mar 02 '17 at 13:56
@Shilly I mean he didn't concatenate filepath properly. – Anoop Yaseen P T Mar 02 '17 at 13:59
I wanted to keep H:mm in text file as well as my message variable. – Pyro Mar 02 '17 at 14:01
oh sorry my fault.... – Anoop Yaseen P T Mar 02 '17 at 14:02

score 0 · Accepted Answer · answered Mar 02 '17 at 13:53

fs.open() is an async function. So your entire loop will run before the first callback actually gets called. By that time i equals channelCOount + 1 and channels[ channelCount + 1 ] is undefined.

You can either wrap the callback into a closure, use a let if you can use ES6, or use fs.openSync()

No output file even though variables are not empty

2 Answers2