Develop Reference

async/await function is not working as descirbed in MDN web docs

I know this questions gets asked a lot and I have looked at many similar ones but haven't been able to solve it. But I wrote my code exactly as described in MDN webdocs for async/await but it's not working as expected. Basically I am trying to seed my mongo database for my express.js application.
const Activity = require('./Models/activity');
const mongoose = require('mongoose');
const faker = require('faker');
function dropDB() {
//Check if collections exist. Drop if they do.
mongoose.connect("mongodb://localhost/auth_demo", { useNewUrlParser: true , useUnifiedTopology: true });
var db = mongoose.connection;
db.once('open', (err, res) => {
mongoose.connection.db.listCollections().toArray(function (err, names) {
// console.log(names); // [{ name: 'dbname.myCollection' }]
if (names.length > 1) {
console.log("db connect");
db.dropCollection('users', (err, res) => {
if (err){
console.log(err);
}else {
console.log("DB dropped sucessfully");
}
})
}
else {
console.log("no collections to drop");
}
});
})
}
function createUsers() {
var usersAdded = new Array();
return new Promise(resolve => {
for (let i = 0; i<20; i++) {
User.register( new User(
{
username: faker.internet.userName(),
name: faker.name.firstName() + " " + faker.name.lastName(),
zipcode: faker.address.zipCode(),
friends: []
}
), faker.internet.password(), (err, user) => {
if (err){
console.log(err)
}
else {
usersAdded.push(user);
}
}
)
};
resolve(usersAdded);
});
}
async function main() {
dropDB();
let x = await createUsers();
return x;
}
const returnedVal = main();
returnedVal.then((x) => console.log(x.length));
// module.exports = main;
This is always what prints to the console:
0,
db connect,
DB dropped sucessfully,
As you can see the console.log() in main() runs before createUsers() has finished running. So the users array is still empty even though it should have 20 users.

How to update a global variable with a sqlite query in javascript?

I want to update a globally declared variable after sqlite query,
but I cant get it to work,
I have read that it might be related to asynchronous functions but I have no idea how to implement callbacks and stuff in this example,
can you guys help please. Here is the code:
const sqlite3 = require('sqlite3').verbose();
const dbPath = './src/db/db.sqlite3';
let db = new sqlite3.Database(dbPath, (err) => {
if (err) {
console.error(err.message);
}
console.log('Connected to database.');
});
let number = null;
let rowsExist = null;
db.get("select count(*) from PRICE", [], (err, row) => {
if (err) {
console.error(err.message)
}
else {
rowsExist = Object.values(row)[0];
console.log(rowExist) //this works but outside the function it doesnt get updated
}
});
// here rowExist remains the same after query
if (rowsExist === null) {
number = 1
}
else {
db.get("SELECT number FROM PRICE ORDER BY number DESC LIMIT 1", [], (err, row) => {
if (err) {
console.error(err.message)
}
else {
number = Object.values(row)[0] + 1
}
})
};

How to return Boolean properly in different NodeJS files?

So I have files inside the following folder:
app/controller/token.js
app/controller/news.js
token.js:
"use strict";
var connection = require("../con");
exports.isTokenExists = function(token) {
var checkToken = "SELECT COUNT(`id`) AS 'total' FROM `user` WHERE `token` = '" + token + "'";
var isExists = false;
var count;
var checkResult;
connection.query(checkToken, function(error, rows) {
if (!error) {
checkResult = JSON.parse(JSON.stringify(rows));
for (var i = 0; i < checkResult.length; i++) {
var row = rows[i];
count = row.total;
}
if (count > 0) {
isExists = true;
}
}
});
return isExists;
};
news.js:
"use strict";
var response = require("../response/responses");
var connection = require("../con");
var getToken = require("./token");
exports.news = function(req, res) {
response.send(false, "News API", null, res);
};
exports.allNews = function(req, res) {
var checkTokenExists = getToken.isTokenExists("75d12cc4dc07608d5b87a6cba33cac056df1239c");
if (checkTokenExists) {
var allNewsQuery = "SELECT a.`id`, b.`title` AS `category`, a.`title`, a.`description`, a.`content`, a.`image`, a.`created_date` FROM `news` AS a LEFT JOIN `news_category` AS b ON a.`id_news_category` = b.`id` ORDER BY `created_date` DESC LIMIT 20";
connection.query(allNewsQuery, function(error, rows) {
if (error) {
response.send(true, "" + error, null, res);
} else {
var data = [];
var newsData = JSON.parse(JSON.stringify(rows));
for (var i = 0; i < newsData.length; i++) {
var row = rows[i];
data[i] = {
id: row.id,
idCategory: row.idCategory,
category: row.category,
title: row.title,
description: row.description,
image: row.image,
createdDate: row.created_date
};
}
response.send(false, "News is not empty", data, res);
}
});
} else {
response.send(true, "Error: Token not found", checkTokenExists, res);
}
};
I always getting false value from isTokenExists meanwhile the token is exists in the table.
How do I get true response if the token is exist and how do I get false response if the token is not exists in table?
Any help will be much appreciated.
Regards.

The issue here is that connection.query accepts a callback, but the rest of your code will move passed that without awaiting the result, which is why your isExists always returns false. You can fix this by encapsulating the query with a Promise like this:
"use strict";
const connection = require("../con");
exports.isTokenExists = async function(token) {
const checkToken = "SELECT COUNT(`id`) AS 'total' FROM `user` WHERE `token` = ?";
return new Promise((resolve, reject) => {
connection.query(checkToken, token, function (error, results) {
if (error) return reject(error);
return resolve(results.length > 0);
});
});
};
I also simplified the logic in the callback a bit.
Then, in news.js await the result like this:
exports.allNews = async function(req, res) {
getToken.isTokenExists("75d12cc4dc07608d5b87a6cba33cac056df1239c")
.then(result => {
if (result === true) {
//place your code for handling if the token exists here
}
else {
//place your code for handling if the token does not exist
}
})
.catch(err => {
//handle error
});
}

You are missing async / await concept. You need to wait until your query executes.
1) Write a promise function
export.getCount = function(query) {
return new Promise((res, rej) => {
let count = 0;
connection.query(checkToken, function(error, rows) {
if (!error) {
checkResult = JSON.parse(JSON.stringify(rows));
for (var i = 0; i < checkResult.length; i++) {
var row = rows[i];
count = row.total;
}
}
return res(count);
})
}
2) Write async function which supports await operations
exports.isTokenExists = async function(token) {
var query = "SELECT COUNT(`id`) AS 'total' FROM `user` WHERE `token` = '" + token + "'";
let count = await getCount(query)
return count > 0; // Returns true if count is > 0
};

Are chrome notifications received via service workers batched or real time?

I am trying to implement Browser Push Notification for my website. I am noticing even though the browser received notification, it doesn't display the notification sometimes.
var showNotification = function (event, data) {
var notificationData = data['data'];
var title = notificationData['title'];
var body = notificationData['body'];
var icon = notificationData['icon'];
var notificationActionsData = notificationData["actions"];
var actions = [];
if(notificationActionsData) {
for(var i=0; i < notificationActionsData.length; i++) {
var action = {
action: "action" + i,
title: notificationActionsData[i].title,
};
actions.push(action);
}
}
var campaignId = notificationData["id"];
self.registration.showNotification(title, {
body: body,
icon: icon,
data: notificationData,
tag: notificationData.id,
actions: actions
});
pushowlReporting.tickle(campaignId, "delivery");
};
function processNotification(event) {
if (event.data) {
var data = event.data.json();
showNotification(event, data);
}
else {
fetch("https://" + hostname + "/api/v1/subdomain/" + subdomain + "/campaign/", {'mode': 'no-cors'}).then(
function (response) {
if (response.status !== 200) {
console.log('Looks like there was a problem. Status Code: ', response.status);
return;
}
// Examine the text in the response
response.text().then(function (responseText) {
var data = JSON.parse(responseText);
showNotification(event, data);
});
}
).catch(function (err) {
console.log('Fetch Error :', err);
}
);
}
}
self.addEventListener('push', function (event) {
event.waitUntil(processNotification(event));
});
My reporting API shows that the notification has been delivered however the browser displays the notification intermittently.
The notification display is quite erratic. Sometimes the notifications will display immediately, while sometimes it doesn't display for a while and all of a sudden all past notifications come in a batch. And at times some notifications don't get displayed at all.
Let me know if am doing something wrong here?

Function passed to event.waituntil should return a promise. If not the scope would be messed up as the lifetime of the event wouldnt have got extended.
https://developer.mozilla.org/en-US/docs/Web/API/ExtendableEvent/waitUntil
var showNotification = function (event, data) {
var notificationData = data['data'];
var title = notificationData['title'];
var body = notificationData['body'];
var icon = notificationData['icon'];
var notificationActionsData = notificationData["actions"];
var actions = [];
if(notificationActionsData) {
for(var i=0; i < notificationActionsData.length; i++) {
var action = {
action: "action" + i,
title: notificationActionsData[i].title,
};
actions.push(action);
}
}
var campaignId = notificationData["id"];
return self.registration.showNotification(title, {
body: body,
icon: icon,
data: notificationData,
tag: notificationData.id,
actions: actions
}).then(function (succ) {
pushowlReporting.tickle(campaignId, "delivery");
});
};
function processNotification(event) {
if (event.data) {
var data = event.data.json();
return showNotification(event, data);
}
else {
return fetch("https://" + hostname + "/api/v1/subdomain/" + subdomain + "/campaign/", {'mode': 'no-cors'}).then(
function (response) {
if (response.status !== 200) {
console.log('Looks like there was a problem. Status Code: ', response.status);
return;
}
// Examine the text in the response
response.text().then(function (responseText) {
var data = JSON.parse(responseText);
showNotification(event, data);
});
}
).catch(function (err) {
console.log('Fetch Error :', err);
}
);
}
}
I have just added return statements to your code. Try this out.

Fetched data from mongodb viewing using ejs trouble

I m creating a job search portal using nodejs,mongodb,and ejs view engine :
collection "filters" = 'username' 'tags'
collection "alljobs" = 'category' 'jobsdata'
In the following code I'm fetching 'tags' from "filters" collection and comparing with all 'category' in "alljobs" collection. And then all 'tags' array matched with 'category' view their respective 'jobsdata' using ejs view engine.
Problem: Code is working but in browser I can't see all matched category respective jobs only one category jobs data viewed. I am not able to understand where is the problem?
Code:
function processRequest(req,res){
var tags,data,jobsdata = [];
var len;
if(condition)
{....}
else{
var db = new Db('askhere', new Server('localhost', '27017'));
db.open(function (err, db) {
db.authenticate('', '', function (err, result) {
var url = 'mongodb://localhost:27017/askhere';
client.connect(url, function (err, db) {
var col = db.collection('filters');
col.find({username:req.session.userName}).toArray(function (err, items) { // find tags of session user from collection filters
console.log('items: ' + JSON.stringify(items));
items.forEach(function (doc) {
tags = doc.tags; //save tags
});
var col = db.collection('alljobs'); //find all categories jobs matched with tags data in collection alljobs
for(var i=0; i<tags.length;i++){
col.find({category:tags[i]}).toArray(function (err, items1) {
if (items1 == false) {
res.render('mainqa',{uname:req.session.userName,tags:'No Tags Selected',jobsdata:'No Tags Matched !!!',len:0});
}
items1.forEach(function (doc1) {
jobsdata = doc1.jobsdata;
var html = ["url : ", "Posted Date : ", "Job Title : ", "Company : ", "Location : "]
for (var i = 0; i < 25; i++) {
for (var j = 0; j < 5; j++) {
data.push(html[j] + jobsdata[i][j]);
} //Nested for loop
} //for loop covert 2D array in 1D
res.render('mainqa',{uname:req.session.userName,tags:tags,jobsdata:data,len:len});
}); //forEach
}); //col.find collection=alljobs
} //for loop
}); //col.find collection=filters
}); //client connect
}); //db.authenticate
}); //db.open
} //else end
} //function processRequest end

You should stop using callbacks for nesting code of multiple methods unless you want to end up with the Callback Hell. Use the async module to simplify this task, in particular you'd need to use async.waterfall() since you want to run multiple tasks that depend on each other.
The async.waterfall() method allows you to pass values between the functions in a trickle-down manner. It is quite handy when you need the results of a previous function to perform an operation with the next function in the series.
Consider restructuring following this example:
var async = require("async"),
userName = req.session.userName,
locals = {},
url = 'mongodb://localhost:27017/askhere',
db = new Db('askhere', new Server('localhost', '27017'));
async.waterfall(
[
// Open db
function(callback) {
db.open(function (err, db) {
if (err) return callback(err);
callback(null, db);
});
},
// Authenticate and connect
function(db, callback) {
db.authenticate('', '', function (err, result) {
if (err) return callback(err);
client.connect(url, function (err, res) {
if (err) return callback(err);
locals.db = db;
callback(null, locals);
});
});
},
// Query filters collection for tags of session user
function(arg, callback) {
var collection = arg.db.collection("filters");
collection.find({"username": userName}).toArray(function (err, result) {
if (err) return callback(err);
locals.tags = result.map(function(item){ return item.tags; });
callback(null, locals);
});
},
// Query alljobs collection for categories jobs matched with tags data
function(arg, callback) {
var collection = arg.db.collection("alljobs");
collection.find({"category": {"$in": arg.tags}}).toArray(function (err, result) {
if (err) return callback(err);
locals.jobsdata = result.map(function (doc){ return doc.jobsdata; });
callback(null, locals);
});
}
], function(err, result) {
if (err) { /* handle err */ };
res.render("mainqa", {
"uname": userName,
"tags": result.tags,
"jobsdata": result.jobsdata
});
});
);