I don't know about the correct title for my problem. I just need a value going out of a function, just like return but I think it's not same.
i have code snippet from controller in adonisjs framework:
var nmeadata = "";
jsondata.forEach(element => {
var x = element.nmea
var buff = new Buffer(x, 'base64')
zlib.unzip(buff, (err, res) => {
if(err)
{
//
}
else
{
nmeadata += "greed island"
nmeadata += res.toString()
}
})
});
return view.render('admin.index', {
data: datanmea.toJSON(),
nmea: nmeadata
})
I need the result of unzipped string data that inserted to nmeadata from zlib function then send it to view. But, for this time, even I cannot displaying a simple output like greed island to my view.
thank you.
UPDATE
Still not working after using promises:
class NmeaController {
async index({view})
{
const datanmea = await NmeaModel.all()
const jsondata = datanmea.toJSON()
var promises = [];
var nmeadata = "";
jsondata.forEach(element => {
promises.push(
new Promise(resolve => {
let x = element.nmea
let buff = new Buffer(x, 'base64')
zlib.unzip(buff,
(err, res) => {
if (err) {
//
} else {
nmeadata += "test add text"
// nmeadata += res.toString()
}
//im also try using resolve() and resolve("any text")
resolve(nmeadata);
})
}
)
)
});
await Promise.all(promises);
return view.render('admin.index', {
data: datanmea.toJSON(),
nmea: nmeadata
});
}
UPDATE AUGUST 22 2019
i'm already tried solution from maksbd19 but still not working
class NmeaController {
async index({view})
{
const datanmea = await NmeaModel.all()
const jsondata = datanmea.toJSON()
var promises = [];
var nmeadata = "";
jsondata.forEach(element => {
promises.push(
new Promise(resolve => {
let x = element.nmea
let buff = new Buffer(x, 'base64')
zlib.unzip(buff,
(err, res) => {
if (err) {
// since you are interested in the text only, so no need to reject here
return resolve("");
}
return resolve("greed island")
})
}
)
)
});
const result = await Promise.all(promises); // this will be an array of results of each promises respectively.
nmeadata = result.join(""); // process the array of result
return view.render('admin.index', {
data: datanmea.toJSON(),
nmea: nmeadata
});
}
}
I'd suggest two things-
modify zlib.unzip callback function to resolve properly;
(err, res) => {
if (err) {
// since you are interested in the text only, so no need to reject here
return resolve("");
}
return resolve(res.toString())
}
retrieve the final data from the result of Promise.all
const result = await Promise.all(promises); // this will be an array of results of each promises respectively.
nmeadata = result.join(""); // process the array of result
In this approach every promise will resolve and finally you will get the expected result in array.
Related
I have a code to fetch directory names from first API. For every directory, need to get the file name from a second API. I am using something like this in my Node JS code -
async function main_function(req, res) {
const response = await fetch(...)
.then((response) => {
if (response.ok) {
return response.text();
} else {
return "";
}
})
.then((data) => {
dirs = ...some logic to extract number of directories...
const tempPromises = [];
for (i = 0; i < dirs.length; i++) {
tempPromises.push(getFilename(i));
}
console.log(tempPromises); // Prints [ Promise { <pending> } ]
Promise.all(tempPromises).then((result_new) => {
console.log(result_new); // This prints "undefined"
res.send({ status: "ok" });
});
});
}
async function getFilename(inp_a) {
const response = await fetch(...)
.then((response) => {
if (response.ok) {
return response.text();
} else {
return "";
}
})
.then((data) => {
return new Promise((resolve) => {
resolve("Temp Name");
});
});
}
What am I missing here?
Your getFilename() doesn't seem to be returning anything i.e it's returning undefined. Try returning response at the end of the function,
async function getFilename(inp_a) {
const response = ...
return response;
}
Thanks to Mat J for the comment. I was able to simplify my code and also learn when no to use chaining.
Also thanks to Shadab's answer which helped me know that async function always returns a promise and it was that default promise being returned and not the actual string. Wasn't aware of that. (I am pretty new to JS)
Here's my final code/logic which works -
async function main_function(req,res){
try{
const response = await fetch(...)
const resp = await response.text();
dirs = ...some logic to extract number of directories...
const tempPromises = [];
for (i = 0; i < dirs.length; i++) {
tempPromises.push(getFilename(i));
}
Promise.all(tempPromises).then((result_new) => {
console.log(result_new);
res.send({ status: "ok" });
});
}
catch(err){
console.log(err)
res.send({"status" : "error"})
}
}
async function getFilename(inp_a) {
const response = await fetch(...)
respText = await response.text();
return("Temp Name"); //
}
I've make a translation service in nodejs :
module.exports = {GetcountryFR, GetRegionFR, GetChildrenFR, GetHomeownFR, GetHomestyleFR, GetIncomeFR, GetLstatusFR, GetWdomainFR, GetWtypeFR, GetSexFR}
async function GetcountryFR(country) {
var countrix = country;
switch (countrix) {
case 'createuser.france': countrix = 'FRANCE'; break;
case 'createuser.belgique': countrix = 'BELGIQUE'; break;
default: countrix = 'UNKNOWN'; break;
}
return countrix;
}
And now I make a function which uses translat function
const translate = require('../services/translate');
exports.AllUserToCSV = async function CSV() {
try {
let user = User.find();
var data = [];
len = user.length;
for (i = 0; i < len; i++) {
let sexix = await translate.GetSexFr(user[i].sex);
let regionix = await translate.GetRegionFR(user[i].region);
let countrix = await translate.GetcountryFR(user[i].country);
let wtypix = await translate.GetWtypeFR(user[i].wtype);
let wdomainix = await translate.GetWdomainFR(user[i].wdomain);
temp = {
sex: sexix,
region: regionix,
country: countrix,
wtype: wtypix,
wdomain: wdomainix,
}
data.push(temp);
}
const csvData = csvjson.toCSV(data, { headers: 'key' })
filename2 = '/assets/media/' + 'TEST' + '.csv';
writeFile(filename, csvData, (err) => {
if (err) {
console.log(err); // Do something to handle the error or just throw it
throw new Error(err);
}
console.log('Success!');
});
} catch (e) {
console.error(e);
}
}
In results CSV file is Empty [].
If I put values in temp it's OK.
Why my translate function didn't work ??
Thanks for Help Good Friends :)
Simply await your call to the User model i.e let user = await User.find();
Also for the loop, try
let users = await User.find();
await Promise.all(users.map(async (user) => {
let sexix = await translate.GetSexFr(user.sex);
...
})));
Writing to file, you may want to use await fs.writeFile(...);. This will make sure file is written before processing the next.
When i create new variable and assign callback function, But data cannot return from callback function. Undefined is occurring at new variable.
const nedb = require('nedb');
const user = new nedb({ filename: './builds/database/users.db', autoload: true });
var s = user.find({}, function (err,docs) {
if(docs.length == 0) {
var data = false;
} else {
var data = docs;
}
return data;
});
console.log(s);
var s is undefined! ....
You are mixing up callback and Promise which are two different way to handle asynchronous calls.
I recommend you to use of Promises because they are simpler and the present and future of javascript.
Using async/await which is the next step after Promises
const user = {
find: () => ['jon', 'kalessi', 'jorah'],
};
async function getUsers() {
return (await user.find({})) || [];
}
async function myJob() {
const users = await getUsers();
console.log(users);
// Put your next code here
}
myJob();
Full promise :
const user = {
find: () => new Promise((resolve) => resolve(['jon', 'kalessi', 'jorah'])),
};
user.find({})
.then((docs = []) => {
console.log(docs);
// Put you next code here, you can use of the variable docs
})
.catch((err) => {
console.log(err);
});
Full callback :
const user = {
find: (_, callback) => callback(false, ['jon', 'kalessi', 'jorah']),
};
user.find({}, (err, docs = []) => {
if (err) {
console.log(err);
} else {
console.log(docs);
// Put you next code here, you can use of the variable docs
}
});
I think user.find returning the promise. you can do like this.
const nedb = require('nedb');
const user = new nedb({ filename: './builds/database/users.db', autoload: true });
var s = user.find({}, function (err,docs) {
if(docs.length == 0) {
var data = false;
} else {
var data = docs;
}
return data;
});
Promise.all(s)
.then(result => {
console.log(result);
});
Otherwise you can also use await Like this:
async function abc(){
const nedb = require('nedb');
const user = new nedb({ filename: './builds/database/users.db', autoload: true });
var s = await user.find({}, function (err,docs) {
if(docs.length == 0) {
var data = false;
} else {
var data = docs;
}
return data;
});
}
because await worked with async thats why i put it into async function.
I am working on a nodejs code that fetches data from a site, parses it, finds particular data and fetches something else for the data that was previously fetched. But the final return statement is returning without the value fetched from the second API call.
I tried to implement async await, but I am not sure where do I have to put them exactly.
const getMainData = async val => {
let result = [];
//get xml data from the API
const xmlData = await getSiteContent(`value`); //axios call
parseString(xmlData, (err, json) => { //convert xml to json
const { entry } = json.feed; // array of results.
result = entry.map(report => {
const secondInfo = getSomeMoreData(report.something); //axios call
const data = {
id: report.id,
date: report.date,
title: report.title
};
data.info = secondInfo;
return data;
});
});
return { result };
};
I was expecting the function to return the array result that has id, date, title and info. But I am getting info as null since it is going to another function that does one more API call.
Try wrapping parseString in a promise so you can await the result, then make the entry.map callback an async function so that you can use the await keyword to wait for the result of the axios fetch.
async function xml2json(xml) {
return new Promise((resolve, reject) => {
parseString(xml, function (err, json) {
if (err)
reject(err);
else
resolve(json);
});
});
}
const getMainData = async val => {
//get xml data from the API
const xmlData = await getSiteContent(`value`); //axios call
const json = await xml2json(xmlData);
const { entry } = json.feed; // array of results
const result = await Promise.all(
entry.map(async report => {
const secondInfo = await getSomeMoreData(report.something); // axios call
const data = {
id: report.id,
date: report.date,
title: report.title,
};
data.info = secondInfo;
return data;
})
)
return { result };
}
Let me know if that works. If not, I can try to help you out further.
The problem with your code is you have mixed promises concept(async/await is a syntactic sugar - so same thing) along with callback concept.
And the return statement is outside callback() of parseString() and the callback would be executed maybe after returning results only because parseString() is an asynchronous function.
So in the following solution I have wrapped parseString() in a promise so that it can be awaited.
const parseStringPromisified = async xmlData => {
return new Promise((resolve, reject) => {
parseString(xmlData, (err, json) => {
if (err) {
reject(err);
}
resolve(json);
});
});
};
const getMainData = async val => {
//get xml data from the API
const xmlData = await getSiteContent(`value`); //axios call
const json = await parseStringPromisified(xmlData);
const { entry } = json.feed; // array of results.
const result = entry.map(async report => {
const secondInfo = await getSomeMoreData(report.something); //axios call
return {
id: report.id,
date: report.date,
title: report.title,
info: secondInfo
};
});
return Promises.all(result);
};
Trying to get the variable random_song from the function functions.random_song
Function:
functions.random_song = () => {
fs.readFile('auto_playlist.txt', 'utf8', function(err, data) {
if (err) {
console.log(`${`ERR`.red} || ${`Error fetching song from auto playlist ${err}`.red}`);
}
let songs = data.split('\n');
songs.splice(-1, 1);
var random = Math.floor(Math.random()*songs.length);
let random_song = (songs[random]);
return random_song;
})
}
Attempting to callback the random song
functions.random_song(song => {
console.log(song)
})
The code just return undefined Ideas?
Your function:
functions.random_song = (callback) => {
fs.readFile('auto_playlist.txt', 'utf8', function(err, data) {
if (err) {
// Do stuff
return callback(err);
}
// Do stuff
callback(null, random_song);
})
}
And then call it:
functions.random_song((err, song) => {
// Do stuff
});
You may want to read more about using Promise/async-await instead of callback.
functions.random_song = () => {
let data = fs.readFileSync('auto_playlist.txt', 'utf8');
let songs = data.split('\n');
songs.splice(-1, 1);
var random = Math.floor(Math.random()*songs.length);
let rand_song = (songs[random]);
return rand_song;
}
console.log(functions.random_song())
got it working, thanks for the help <3
Following is the code which use Promise to handle file read and data processing task asynchronously
const fs = require('fs')
const functions = {}
functions.random_song = () => {
return new Promise((resolve, reject) => {
fs.readFile('auto_playlist.txt', 'utf8', function(err, data) {
if (err) {
console.log(err)
reject(err)
}
let songs = data.split('\n');
songs.splice(-1, 1);
var random = Math.floor(Math.random()*songs.length);
let random_song = (songs[random]);
resolve(random_song);
})
})
}
functions.random_song()
.then(song => console.log('Song Name', song))
.catch(err => console.error('Error fetching songs', err))
console.log('It will be executed before promise is resolved')
fs.readFile is asynchronus and your function will return before the file is read. Use fs.readFileSync instead. Like this:
functions.random_song = () => {
const data = fs.readFileSync('auto_playlist.txt', 'utf8');
let songs = data.split('\n');
songs.splice(-1, 1);
var random = Math.floor(Math.random()*songs.length);
let random_song = (songs[random]);
return random_song;
}