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Undefined errors using Node.js, Mongoose, and Discord.js [Cannot read property of undefined]

I've been scouring similar problems but haven't seem to have found a solution that quite works on my end. So I'm working on a Discord bot that takes data from a MongoDB database and displays said data in the form of a discord embedded message using Mongoose. For the most part, everything is working fine, however one little section of my code is giving me trouble.
So I need to import an array of both all available users and the "time" data of each of those users. Here is the block of code I use to import said data:
for (i = 0;i < totalObj; i++){
timeArray[i] = await getData('time', i);
userArray[i] = await getData('user', i);
}
Now this for loop references a function I made called getData which obtains the data from MongoDB by this method:
async function getData(field, value){
var data;
await stats.find({}, function(err, result){
if(err){
result.send(err);
}else{
data = result[value];
}
});
if(field == "user"){
return data.user;
}else if (field == "time"){
return data.time;
}else{
return 0;
}
So that for loop is where my errors currently lie. When I try to run this code and display my data through a discord message, I get this error and the message does not get sent:
(node:13936) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'time' of undefined
Now the strange thing is, this error does not happen every time. If I continue calling the command that triggers this code from my discord server, it's almost like a 50/50 shot if the command actually shows the message or instead gives this error. It is very inconsistent.
This error is confounding me, as the undefined part does not make sense to me. The objects that are being searched for in the mongoDB collection are definitely defined, and the for loop never exceeds the number of objects present. My only conclusion is that I'm doing something wrong with my asynchronous function design. I have tried altering code to use the getData function less often, or to not use awaits or asynchronous design at all, however this leaves my final discord message with several undefined variables and an eventual crash.
If anyone has any advice or suggestions, that would be very much appreciated. Just for reference, here is the full function that receives the data, sorts it, and prepares a string to be displayed on the discord server (though the error only seems to occur in the first for loop):
async function buildString(){
var string = "";
var totalObj;
var timeArray = [];
var userArray = [];
var stopSort = false;
await stats.find({}, function(err, result){
if(err){
result.send(err);
}else{
totalObj = result.length;
}
});
for (i = 0;i < totalObj; i++){
timeArray[i] = await getData('time', i);
userArray[i] = await getData('user', i);
}
while(!stopSort){
var keepSorting = false;
for(i = 0; i < totalObj ; i++){
var target = await convertTime(timeArray[i]);
for(j = i + 1 ; j < totalObj ; j++){
var comparison = await convertTime(timeArray[j]);
if(target > comparison){
//Switch target time with comparison time so that the lower time is up front
var temp = timeArray[i];
timeArray[i] = timeArray[j];
timeArray[j] = temp;
//Then switch the users around so that the user always corresponds with their time
var userTemp = userArray[i];
userArray[i] = userArray[j];
userArray[j] = userTemp;
//The loop will continue if even a single switch is made
keepSorting = true;
}
}
}
if(!keepSorting){
stopSort = true;
}
}
//String building starts here
var placeArray = [':first_place: **1st', ':second_place: **2nd', ':third_place: **3rd', '**4th', '**5th', '**6th', '**7th', '**8th', '**9th', '**10th'];
for(i = 0; i < totalObj; i++){
string = await string.concat(placeArray[i] + ": " + userArray[i] + "** - " + timeArray[i] + " \n\n");
console.log('butt');
}
console.log("This String:" + string);
return string;
}

I think problem is you are trying to await function with callback, it will not work => access to data.time may run before data = result[value]. If you need await callback, you can use custom Promise (or use util.promisify, more info here)
Promise:
function findStats(options) {
return new Promise((resolve, reject) => {
return stats.find(options, function (err, result) {
if (err) {
return reject(err)
}
return resolve(result)
})
})
}
utils.promisify
const util = require('util');
const findStats = util.promisify(stats.find);
Now you can use await in your function
async function getData(field, value) {
try {
const result = await findStats({})
const data = result.value
if (field === 'user') {
return data.user
}
if (field === 'time') {
return data.time
}
return 0
} catch (error) {
// here process error the way you like
// or remove try-catch block and sanitize error in your wrap function
}
}

Get and check a value from JSON read in NodeJS

I'm trying to check if a user exists (registered on a json file).
Unfortunately I don't find a valid solution in all Stack Overflow that gives me a simple "true" in a callback.
The version closest to a solution
Experiment V1 :
let userExist;
function check(){
console.log("CHECK!");
return userExist = true;
}
// check(); if this, return true... obvious.
//// check if user exist
server.readFileSync(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if ( userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check(); // return undefined ???
}
}
});
console.log("userExist value : "+userExist);
differently formulated the debugs also appear, but "true" never returns.
note: yes, JSON is read correctly. If everything works inside the readfile, you immediately notice the same emails.
output: "undefined"
Log: total bypassed
Experiment V2 :
In this case (with asynchronous reading) it returns all the debugging (but the "true" remains undefined)
The problem with the asynchronous is that I have to wait for it to check to continue with the other functions.
//// check if user exist
server.readFile(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if (/* json.allusers.hasOwnProperty(key) &&*/ userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check();
}
}
});
var userExist;
function check(userExist){
console.log("CHECK!");
return userExist=true;
}
console.log("userExist value : "+userExist+"");
server listening on: 8080
userExist value : undefined
CHECK!
FINDED EQUAL
Experiment V3 :
after the various suggestions I come to a compromise by using the syntax for the async functions.
This allowed to reach an ordered code, but despite this it is not possible to wait for the results and export them out of the same function (this is because node itself is asynchronous! Therefore it has already gone on!)
using a "message" variable to check if it could return an object I did so:
//simple output tester
var message;
// create a promise
let loopusers = new Promise( (resolve)=>{
server.readFile( filepath, 'utf8',
(err, data) => {
let json = JSON.parse(data),
userlist = json.allusers,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
// loop all items
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : user isn't free");
findedequal=true;
resolve(true); // return the result of promise
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
resolve(false); // return the result of promise
}
}
// call the action
createuser();
});
});
// when promise finished --> start action
async function createuser(message)
{
let userExist = await loopusers;
console.log("userExist: "+userExist);
if(userExist)
{
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
message = { Server: "Registration user -> completed..."};
}
// return values
return message;
};
It is also possible to use the classic syntax via "then". For exemple:
//simple output tester
var message;
// create a promise
let loopusers = new Promise( (resolve)=>{
...
});
loopusers.then( (response)=>{
...
})
Then I realized that it was easy to simplify even more by calling the functions directly from the initial one:
var message;
// create a promise --> check json items
server.readFile( filepath, 'utf8',
(err, data) => {
let json = JSON.parse(data),
userlist = json.allusers,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : user isn't free");
findedequal=true;
createuser(true); // call direct function whit params true
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
createuser(false); // call direct function whit params false
}
}
});
// start action
function createuser(userExist)
{
if(userExist)
{
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
message = { Server: "Registration user -> completed!"};
}
// return values
return message;
};
debugging is taken and written
the message is lost outside the aSync function
Experiment V4 Final! :
Finally, after many attempts the solution! (Yes... But know it's not Async)
If we allocate in a variable the reading becomes synchronous the whole model and we return to the simple one
let message,
file = server.readFileSync(filepath, 'utf8'), // read sync
json = JSON.parse(file), // now parse file
userlist = json.allusers, // get your target container object
userExist,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : finded equal value on key ["+key+"] - user isn't free");
findedequal=true;
userExist = true;
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
userExist = false;
}
}
if(userExist)
{
console.log("└ EXIT TO CHECK --> Can't create user, function stop.");
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
console.log("└ Exit to check --> New user registration ...");
message = { Server: "Registration user -> completed!"};
}
}
return message;
Now:
It's all sync and all log is perfect
all var is checked
all return... return
** Final conclusions: **
Is it possible to retrieve an ASync variable in node?
As far as I understand so far ... no.
Node is async by its nature, therefore recovering information that is not saved and then recovered from a DB is left behind among the things to do, becoming unrecoverable if you use it as in this post.
However ... if the purpose is to make reading a file synchronous, the answer was simpler than expected.
A special thanks to: Barmar; Austin Leehealey; C.Gochev;

The problem is that you are calling console.log("userExist value : "+userExist+"");
too early. At the moment that you call that line, userExist is not defined yet. This is because the server.readFile() function requires a callback and that callback function is executed once it has read the file. However, reading files often take time and so the program keeps going. It executes console.log("userExist value : "+userExist+""); and then goes back to the callback function and defines userExist as true.
If you want more information on what callbacks are look at the link below. Callbacks are a defining feature of Nodejs and understanding them is essential to any Node website.
https://medium.com/better-programming/callbacks-in-node-js-how-why-when-ac293f0403ca
Try something like this.
let userExist;
function check(){
console.log("CHECK!");
return userExist = true;
}
// check(); if this, return true... obvious.
//// check if user exist
server.readFileSync(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if ( userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check(); // return undefined ???
console.log("userExist value : "+userExist);
}
}
});

fs.write & read not updating

Basically, my code here is saying that if a user sends a message !submit ___ then the file leaderboard.json will up their count by one.
This all works perfectly however say for example their count goes from 0 to 1, the next time that same person sends !submit, their count should go from 1 to 2 without me having to restart the script every time. This isn't happening unfortunately... I send !submit and my count goes from 0 to 1, but then I send it again and it stays going from 0 to 1.
Leaderboard.json:
{
"usercount<#386679122614681600>": 0
}
index.js:
client.on('message', msg => {
if (msg.content.startsWith("!submit ")){
var shoe = msg.content.substr("!submit ".length);
var fs = require('fs')
fs.readFile('leaderboard.json', 'utf8', function (err,data) {
if (err) {
return console.log(err);
}
var user = msg.member;
var usercount = 'usercount'+user
var username = 'usercount'+user
var LEADERBOARD = require('./leaderboard.json');
var countvalue = LEADERBOARD[username]
var countvalue2 = countvalue+1
var replacetext = ('"'+usercount+'": '+countvalue).toString()
var newtext = ('"'+usercount+'": '+(countvalue2)).toString()
fs.writeFile('leaderboard.json', data.replace(replacetext, newtext),
'utf8', function () {
if (err) return console.log(err);
});
console.log('NEW SUBMISSION: '+replacetext+' >>>> '+newtext)
});
}
Here is what my console looks like after sending !submit twice:
When technically the second line should go from 1 to 2, without me having to close and restart the script.
I know this may seem a bit complicated but any help would be appreciated!

This is what I'd suggest:
const fs = require('fs')
client.on('message', msg => {
if (msg.content.startsWith("!submit ")) {
let shoe = msg.content.substr("!submit ".length);
// read leaderboard file and parse the JSON into a Javascript object
fs.readFile('leaderboard.json', 'utf8', function(err, data) {
if (err) {
console.log("Error reading leaderboard.json", err);
return;
}
let leaderboard;
try {
leaderboard = JSON.parse(data);
} catch(err) {
console.log("Error parsing leaderboard JSON", err);
return;
}
const user = msg.member;
const username = 'usercount' + user;
// make sure there's a count for this username
let cnt = leaderboard[username];
if (!cnt) {
cnt = 0;
}
// increment the cnt
++cnt;
// set the new count
leaderboard[username] = cnt;
// now write the data back to the file
fs.writeFile('leaderboard.json', JSON.stringify(leaderboard), 'utf8', function() {
if (err) {
console.log(err);
return;
}
console.log(`New Submission for ${username}, cnt = ${cnt}`);
});
});
}
});
Summary of changes:
Reads leaderboard.json only once using fs.readFile()
After reading the data, it converts it to JSON using JSON.parse().
Initializes user cnt if not already in the file
Updates cnt in the Javsacript object directly
Writes out the changed object using JSON.stringify() to convert the object back to JSON
Puts new submission console message in fs.writeFile() success handler
Switch to const and let from var
Issues not yet incorporated:
Concurrency issues if multiple message events can be "in-flight" at once and conflict.
More complete error handling besides just stopping processing when there's an error (I'm not sure what your application should be doing in that case as that is application-specific).
Your shoe variable is not being used anywhere, not sure what it's doing there.

How to execute node.js protoype function from html?

I have a program that will work to start a motion sensor when running the file from the command line, but when I try to call the function from HTML, it recognizes the prototype as 'undefined' and will not execute.
Here is the full code:
var sleep = require('sleep');
var Gpio = require('onoff').Gpio;
var LED = new Gpio(18, 'out');
var sensor = new Gpio(17, 'in', 'both');
sensor.watch(function(err, value){
if (err){
console.log('error');
exit();
}
if(value == 1) {
console.log('Motion Detected');
LED.writeSync(value);
sleep.sleep(3);
}
else if(value == 0) {
console.log('No Motion');
LED.writeSync(value);
sleep.sleep(3);
}
});
function exit() {
LED.unexport();
sensor.unexport();
process.exit();
}
dev tools says 'sensor' is undefined.
How do I run sensor.watch(callback) from html?
Thanks!

Executing functions in a loop in javascript

I'm clearly missing something in Java Script. I'd like to execute the same function with different parameters sequentially in a for loop (like in the commented part of code).
I'm instead using callback, but I guess it's not the nicest way, and not flexible, for example if I had more paths to be looped over. What the cleanest approach in sewuentially executing functions?
var data = '';
var filepath = ['path1', 'path2'];
somefunction(filepath, callback) {
//dosth ();
callback();
}
//filepath = ['path1', 'path2'];
//for ( var i = 0; i < filepath.length; i = i + 1 ) {
// somefunction( filepath[i] );
//}
somefunction( filepath[0] , function() {
console.log("Finished processing file 1");
countFromFile( filepath[1], function() {
console.log("Finished processing file 2");
saveToFile( data );
});
});

Use async to make foreach with asynchronous function.
Example:
filepath = ['path1', 'path2'];
async.each(filepath, somefunction, function(err){
// if any of the saves produced an error, err would equal that error
});