Facing issue for synchronous operation in NodeJS - node.js

Question

Below code have 2 files and having client.js which calls to server file but didn't get the synchronous output.
I tried with promise, bluebird, async_await but didn't get success.
Expected output is a sequence of the alphabet in a console.
Do not use settimout.
Understanding of files.
server.js : server file is having NodeAPI which content only routing.
Client.js : logic which tried is in this file
You need to use two console, first run server.js and second console need to run client.js and output will be print in server.js console.
Expecting output is
a
b
c
d
e
/////////////////server.js/////////////////
var express = require('express');
var bodyParser = require('body-parser')
var app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
extended: true
}));
app.post('/', function (req, res) {
console.log(req.body.test)
res.status(200).send('ok');
});
var server = app.listen(3000, function () {
console.log('ok');
});
//////////////client.js///////////////////
//var Promise = require('bluebird');
var request = require('request');
console.log('server file called');
var array_data = ['a', 'b', 'c', 'd', 'e'];
// var promises = [];
// for(let i = 0; i < array_data.length; i++) {
// var promise = request.post({url: 'http://localhost:3000',form : {key:array_data[i]}});
// }
// var page = 0;
// var last_page = array_data.length;
// (function loop() {
// if (page < last_page) {
// request.post({
// url: 'http://localhost:3000',
// form: 'test=' + array_data[page]
// }, function (error, response, body) {
// page++;
// loop();
// });
// }
// }());
// async function loopAsync() {
// for (let i = 0; i < array_data.length; i++) {
// await request.post({
// url: 'http://localhost:3000',
// form: 'test=' + array_data[i]
// });
// }
// }
// loopAsync();
async function loopAsync() {
var page = 0;
var last_page = array_data.length;
while (page < last_page) {
await request.post({
url: 'http://localhost:3000',
form: 'test=' + array_data[page]
});
page++;
}
}
loopAsync();
[enter image description here][1]
[1]: https://i.stack.imgur.com/WVlut.png

Answer 1

You can use util.promisify.
Here is sample code
const reqpost = util.promisify(request.post);
async function loopAsync() {
var page = 0;
var last_page = array_data.length;
while (page < last_page) {
await reqpost({
url: 'http://localhost:3000',
form: 'test=' + array_data[page]
});
page++;
} }
loopAsync();

Answer 2

request.post is a function that takes request options and a callback like this.
function request(letter, callback = () => {}) {
setTimeout(() => {
console.log(letter);
callback();
}, Math.random() * 1000);
}
What you're doing is calling that function without supplying a callback:
async function clientWithRequest() {
const letters = ['a', 'b', 'c'];
for(let i = 0; i < letters.length; i++) {
await request(letters[i]);
}
}
here, the requests are all fired off at the same time and will return in an indeterminate order.
What you need to do if you want to use async is make your request return a promise. Under the hood, await is really just doing request.then(somethingElse()). So if you change your request to return a promise like:
function requestPromise(letter) {
return new Promise((resolve, reject) => {
setTimeout(() => {
console.log(letter);
resolve();
}, Math.random() * 1000);
});
}
your await code will then work as expected. Effectively it's doing.
request('a').then(() => request('b')).then(() => request('c'));

Answer 3

https://github.com/request/request#forms
Since you are forming the form data string yourself via Node
Is it possible that if you can just let request help you form the encoded string via their form method?
const jobs = [];
const array_data = [
'a',
'b',
'c',
'd',
'e',
];
require('request');
const request = require('request-promise');
async function loopAsync() {
for(const char of array_data) {
jobs.push(
request.post({
url: 'https://marble-scene.glitch.me/',
form: {
test: char
}
})
);
}
const output = await Promise.all(jobs);
output.forEach(char => console.log(char)); // # a b c d e
}
loopAsync();
[Edit]
Just edit the client.js code, fixed the silly syntax error inside the jobs.push block
Working prove: https://glitch.com/edit/#!/marble-scene

Answer 4

As an alternative to importing additional libraries. you can simply "promisify" the callback dependent request.post method.
async function loopAsync() {
var page = 0;
var last_page = array_data.length;
while (page < last_page) {
await new Promise((resolve, reject) => {
request.post({
url: 'http://localhost:3000',
form: 'test=' + array_data[page]
}, function(err,httpResponse,body){
if (err) reject(err);
else resolve({httpResponse,body});
});
page++;
});
}
}
loopAsync()

Answer 5

As I did the R&D, request module is not returned promise so for that need to use request-promise library.
let request = require('request');
let rp = require('request-promise');
var array_data = ['a', 'b', 'c', 'd', 'e'];
//with the use of request-promise library
async function loopAsync() {
var page = 0;
var last_page = array_data.length;
while (page < last_page) {
var options = {
method: 'POST',
uri: 'http://localhost:3000',
body: {
test: array_data[page]
},
json: true // Automatically stringifies the body to JSON
};
await rp(options);
page++;
}
}
loopAsync();