Reading and writing to file is non-blocking in my code. Why? - node.js

Question

I'm working on a bot used for Twitch Song Requests. The bot will read the Twitch chat, search for !sr command and get the name of the song. Then, it will search for the song in Spotify, get the URI of the song and add it in the streamer's playlist.
EDIT: I'm sorry if there are any "dumb" code problem (like the callback #ippi notified), I'm really new to programming and Node JS especially.
I now have two functions: one that is searching for the song and writing the received URI in a text file, and one getting the URI from the file. Here's the code:
main code (call of the two functions):
testSong(commandName, accessToken);
let uri = getUri();
console.log(uri);
search for the song:
function testSong(song, accessToken) {
let song1;
let song2;
song1 = song.replace("!sr", "");
song2 = song1.trim();
var uri = "";
axios.get('https://api.spotify.com/v1/search?q=' + encodeURIComponent(song2) + '&type=track&market=CH&limit=1', {
headers: {
Authorization: 'Bearer ' + accessToken
}
})
// handle success
.then(function (response) {
uri = response.data.tracks.items[0].uri;
console.log("yeet")
fs.writeFileSync('conf/uri.txt');
logger.log('info', 'Successfully obtained URI for track ' + song2);
})
// handle error
.catch(function (error) {
logger.log('error', 'Error while accessing Spotify.');
return error;
});
}
get the URI:
function getUri() {
try {
return fs.readFileSync('conf/uri.txt', 'utf-8');
} catch (e) {
logger.log('error', 'Error while reading the URI text file: ' + e.stack);
}
}
I'm having a problem at the reading time. When running the bot for the first time, the uri.txt file is empty.
When I'm sending the first !sr in the Twitch chat, the song is not added in the Spotify playlist beacause it seems that the testSong command is writing to text file AFTER the getUri function read the file.
Even after that, I have to send a new !sr to add the first song, so every request is shifted.
Any idea why this is happening ?
I've read about async functions, but as far as I've understood, it's not what I want because I want the execution of the program to be blocked when I'm writing to the text file, thus the getUri function can then read the current requested song URI, and not be shifted.
EDIT 2: as Felix said, I modified the code as follow:
testSong(commandName, accessToken).then(() => console.log(getUri()));
function testSong(song, accessToken) {
let song1;
let song2;
song1 = song.replace("!sr", "");
song2 = song1.trim();
var uri = "";
return axios.get('https://api.spotify.com/v1/search?q=' + encodeURIComponent(song2) + '&type=track&market=CH&limit=1', {
headers: {
Authorization: 'Bearer ' + accessToken
}
})
// handle success
.then(function (response) {
uri = response.data.tracks.items[0].uri;
console.log("yeet")
fs.writeFileSync('conf/uri.txt', uri, function (err) {
if (err) {
return console.log(err);
} else {
response = true;
}
});
logger.log('info', 'Successfully obtained URI for track ' + song2);
})
// handle error
.catch(function (error) {
logger.log('error', 'Error while accessing Spotify.');
return error;
});
}
Is that correct?

Answer 1

As I have already mentioned in my comments, you are having this problem because you are using promises, i.e. the file will be written some time in the future, after you are trying to read.
And as we discussed, there is no need to use a file to "transfer" the value at all. You can just return the value from testSong (wrapped in a promise):
function testSong(song, accessToken) {
song = song.replace("!sr", "").trim();
return axios.get('https://api.spotify.com/v1/search?q=' + encodeURIComponent(song2) + '&type=track&market=CH&limit=1', {
headers: {
Authorization: 'Bearer ' + accessToken
}
})
// handle success
.then(function (response) {
return response.data.tracks.items[0].uri;
});
// errors should probably be handled by the caller
}
and then:
testSong(commandName, accessToken)
.then(function(uri) {
console.log(uri);
})
.catch(function(error) {
// handle error
});
An async function makes working with promises a bit easier. So you could implement testSong also as
async function testSong(song, accessToken) {
song = song.replace("!sr", "").trim();
const response = await axios.get('https://api.spotify.com/v1/search?q=' + encodeURIComponent(song2) + '&type=track&market=CH&limit=1', {
// ^^^^^
headers: {
Authorization: 'Bearer ' + accessToken
}
});
return response.data.tracks.items[0].uri.
}