Why promise.resolve wait forever in this case? - node.js

Question

I am a nodejs's newbie. I'm testing a promise and have an issue.
Here's my issue.
var express = require('express');
var app = express();
var bodyParser = require('body-parser');
app.use(bodyParser.json());
app.get('/', async function(req,res){
console.log(222);
res.send("Hello!!!");
let check;
try {
console.log(3333);
check = await test();
console.log(4444);
} catch (err) {
console.log("Error : ", err);
}
console.log(111, check);
});
function test () {
return new Promise (resolve => {
console.log(5555);
app.get('/test', function(req, res) {
count = count + 1;
res.send(count.toString());
resolve("hahahaha");
})
})
}
app.listen(9000, function(){
console.log("hehehehe");
});
In a get 'http://localhost:9000' callback, I wait for 'http://localhost:9000/test' result to do something. The thing is, it's working fine for the first time. But since the 2nd, the promise.resolve() function doesn't work.
Here is my first time log:
hehehehe
222
3333
5555
4444
111 'hahahaha'
And here is my second time log :
222
3333
5555
the promise.resovle() doesn't work. It's waiting forever and I don't understand.
EDIT : Here is the solution for using EventEmitter to do signup and smsVerifyCode after modified by the help of Mr. #Aritra Chakraborty
var express = require('express');
var userControler = require('../Controler/user');
var router = express.Router();
var utils = require('../Helper/Utils');
var user_model = require('../Models/user');
const TIMEOUT_VERIFY = 300000;
const CODE_EXPIRED = 0;
const CODE_VALID = 1;
const CODE_INVALID = 2;
const CONTACT_EXISTED = 3;
const DATABASE_ABUSED = 4;
const events = require('events');
const emitter = new events.EventEmitter();
function timeout_verify_sms_emitter (time) {
setTimeout(() => {
emitter.emit('timeout_sms');
}, time);
}
function verify_code(codeGen) {
return new Promise((resolve, reject)=>{
emitter.on("verifySMS", (data)=>{
if (data === codeGen) {
resolve(CODE_VALID);
}
else {
resolve(CODE_INVALID);
}
})
emitter.on('timeout_sms', () =>{
resolve(CODE_EXPIRED);
});
})
}
router.get('/',function(req,res){
res.send("Welcome to the Earth!!!");
})
router.post('/signup', async function(req,res){
let verifyCode;
let checkContact;
let codeGen = utils.generateCode();
try {
checkContact = await user_model.checkContact(userData.contact);
if (checkContact === true) {
res.send(CONTACT_EXISTED);
}
else {
//call send sms to contact function here
//exam : sendSMS(contact)
//
timeout_verify_sms_emitter(TIMEOUT_VERIFY);
verifyCode = await verify_code(codeGen);
}
}
catch (err) {
console.log("Error : ", err);
}
if (verifyCode === CODE_EXPIRED) {
res.send(CODE_EXPIRED);
}
else if (verifyCode === CODE_VALID) {
var result = userControler.processUserData(req.body);
if (result) {
res.send(CODE_VALID);
}
else {
res.send(DATABASE_ABUSED);
}
}
else {
res.send (CODE_INVALID);
}
})
router.post('/signup/verifySMS', function(req, res){
emitter.emit("verifySMS", req.body.smsCode);
})
module.exports = router;

Answer 1

According to the above code:
Whenever you do a get request to / you are CREATING a /test path.
So, the first time it works because /test path has one handler.
Second or more time it doesn't works because,
The /test route has multiple handler now.
How express works is, routes get executed according to their declaration time. (Think middlewares)
Now, Second time the /test will have 2 handlers. And when you hit /test the first handler runs. And as this is not a middlware it doesn't go to the next handler. Now, the first handler has a different resolve function then the second one. So the second resolve function doesn't run at all.(Think closure)
For what are you trying to do most web implementations use long polling. Because if you wait too long for the second route it will throw a timeout error. Means you periodically hit an api to get the status of something. Means you create 3 routes.
A main route, like /signup
A second route like /sendsms
A third route where you send a particual identifier and it returns some positve/negative value. like /sendsms/check, where you might pass the phone number.
Otherwise if you don't care about timeouts you can use EventEmitter inside the /test route.
EDIT1:
var express = require('express');
var app = express();
var bodyParser = require('body-parser');
app.use(bodyParser.json());
const events = require('events');
const emitter = new events.EventEmitter();
let count = 0;
app.get('/', async function (req, res) {
console.log(222);
res.send("Hello!!!");
let check;
try {
console.log(3333);
check = await test();
console.log(4444);
}
catch (err) {
console.log("Error : ", err);
}
console.log(111, check);
});
app.get('/test', function (req, res) {
count = count + 1;
emitter.emit("test",count.toString());
res.send(count.toString());
})
function test(){
return new Promise((res)=>{
emitter.on("test", (data)=>{
res(data);
})
})
}
app.listen(9000, function () {
console.log("hehehehe");
});
EDIT2:
Regarding the solution, you need to handle the timeout differently. Let's say your timeout is 3sec. And the SMS route took 100sec to get a response or maybe it didn't even got a response. Then your function will be stuck there.
function test(sendSMSTime) {
return new Promise((res, rej) => {
emitter.on("test", (data) => {
.
.
res(data);
})
emitter.on('timeout', rej);//On timeout it will run.
})
}
function timeoutEmitter(timeout) {
setTimeout(() => {
emitter.emit('timeout');
}, timeout)
}
app.post('/signup', async function (req, res) {
try {
timeoutEmitter(3000);
.
.
}catch{
}
});