Mongooses, Callbacks, and Bears, oh my! I'm having trouble accessing the values

Greetings everyone,

I find myself stuck in a callback nightmare while attempting to retrieve basic values from a Mongoose count by passing a {query}. Although I can access the value and see it fine in the console within the callback, extracting it from an asynchronous callback setup is proving to be quite challenging.

Using Node.js and Express, I am trying to accomplish simple tasks such as fetching a count of a specific number from my Model, 'Job', with the aforementioned query.

I have a similar situation that works in one instance of a router.get, where I am able to write to a variable outside the callback parent function. Here's an example:

router.get('/repairmanager', ensureAuthenticatedAdmin, function(req, res) {
    var list = [];  // The list populates successfully even within the Job.find callback nest hole

    if(filter == 'userid' && query != "" || null){

        Job.find( {'userid' : new RegExp('^'+query+'$', "i")} )
          .then(function(doc){
            doc.forEach(function(job){
                list.push(job);   
            });  
          }); 
          res.render('repairmanager', { history: { 'data': list}});
    }
)};

The above code works well and the list array gets populated...

However, when I try to obtain another value from

function pendingCount(){

   var test = null;

   Job.count({'repairstatus': 'Pending Approval'}, function(err, cb){
       test = cb;
       console.log('test inside callback: ' + test);
   });
   console.log('test outside callback:  ' + test);
   return test;
};

I struggle to get the `test` variable to populate or return to the pendingCount() function at all.

I understand there is some complexity involved with asynchronous callback functions, but why is the `list` array visible and writable in the other Mongoose function, while not in this function where I'm trying to get a simple count of the query {"repairstatus": "Pending Approval"}?

Thank you for any helpful insights that can assist in resolving this issue.

Answer №1

There is no guarantee that the list will render correctly in the initial example. The rendering success is more by chance due to a race condition between the promise of Job.find and res.render, with res.render currently winning the race. Different network conditions, hardware conditions, or other random factors could change this outcome.

To ensure that res.render is consistently called at the correct time every time, precautionary measures need to be taken.

In the first scenario, moving res.render into the then callback is recommended:

Job.find( {'userid' : new RegExp('^'+query+'$', "i")} ).then( function(doc){

    //console.log(doc);
    doc.forEach(function(job){
        list.push(job);    
    });  

    // render here
    res.render('repairmanager', { history: { 'data' :list}} ); 
}); 

In the second example, returning test directly is not possible since it is populated asynchronously. Instead, return a Promise that resolves to the desired value.

For Mongoose versions >= 4.0, count method returns a Promise by default, so just return the result of count:

function pendingCount(){
    return Job.count({'repairstatus': 'Pending Approval'});
};

Utilize pendingCount as a Promise:

pendingCount().then(function(count) {
    console.log(count);
});

Implementing these adjustments will eliminate any race conditions in the code, ensuring consistent execution timing.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Make the current tab the active tab with the help of AngularJS

I have a set of five tabs that are functioning correctly. However, when I refresh the page, the active tab reverts back to its default state instead of staying in its current active state. Can anyone help me identify where I may be making a mistake? Here ...

AngularJS - sorting JSON data based on key values

I am working with a JSON data set that I need to filter based on the selected option value. The select input is bound to an ng-model, but for some reason, the filter isn't functioning properly. Can anyone spot what mistake I might be making? This is ...

Choosing multiple options from a list

I am working on a messaging app where users can compose and send messages to contacts. Currently, I am only able to send messages to one contact at a time. My goal is to enable users to select multiple contacts to create group messages. Since I am new to a ...

`What is the best way to employ the Return statement in programming?`

Trying to grasp the concepts of functions and methods has been a challenge for me. I often find myself confused about when, where, and how to use return statements in different situations. To illustrate this confusion, let's take a look at two code sn ...

The app running in node.js encountered a "connection timed out" error

Whenever I try to run my Node.js app by executing "node app.js" and setting NODE_ENV to production, it doesn't seem to be recognized as production. Instead, I encounter a connection timeout error when trying to run the app. My goal is to establish a c ...

The hamburger menu unexpectedly appears outside the visible screen area and then reappears at random intervals

My website has a hamburger menu for mobile devices, but there's a problem. When the page loads on a small screen, the hamburger menu is off to the right, causing side scrolling issues and white space. I thought it might be a CSS problem, but after exp ...

The distortion of Blender animation becomes apparent once it is imported into three.js

I've been working on a project where I'm incorporating animations into a scene using a combination of blender and three.js. It took me several hours of trial and error to finally get the model and animation successfully imported into three.js. I ...

Embedding Google+ Sharing in an iframe

I'm currently working on a web application that needs to be compatible with PC, tablets, and mobile phones. I'm interested in integrating Google+ Sharing into the app. However, it appears that when using the url , there are issues with blocking ...

Ways to initiate a page redirection within the componentWillReceiveProps lifecycle method

When my webpage or component generates a form and sends it to the backend API upon submission, I receive an object in return if the process is successful. This object is then added to my redux store. In order to determine whether the reducer successfully ...

Implementing Promises in AngularJS Controller: A Comprehensive Guide

I'm currently working on implementing a basic function using promises in one of my controllers to make sure it works correctly before adding more complex functionality. I keep running into a "TypeError: undefined is not a function" error when trying t ...

React:error:unexpected punctuation

I encountered an issue with this code within the render() function, specifically on the line where I am returning a value and it shows an unexpected token error. Here's the snippet of the code. class PuzzleGame extends React.Component { construct ...

Prevent automatic scrolling to anchors when using router.push() in Next.js

When using the latest version 10.2 of next, every time a URL with a hash is pushed to the router, next.js automatically jumps to the anchor element. import {useRouter} from 'next/router' router.push('/contact#about-us'); This behavior ...

The expected functionality of sending files via ajax is not happening as anticipated

I am having issues with passing file data along with other inputs to my ajax function. Despite my best efforts, the server is not receiving the files. I'm fairly new to using ajax and Jquery. Below is the code snippet of what I have attempted so far. ...

Displaying AJAX data in a table format, showcasing 10 rows of information

I am currently working on an ajax function that retrieves data from a database based on the entered information. My goal is to display this information in a table with the following format: System Id | Last Name | First Name | Middle Name | Address Below ...

Handle 404 errors using the app.use((err, req, res, next) => {}) function and app.use("*", (err, req, res, next) => {}) method without explicitly setting a 404 return

app.use("/login", login); app.use("*", (err: any, req: Request, res: Response, next: NextFunction) => { console.log('error message') res.send('ERROR 404 Not Found') }); app.use((err: any, req: Request, res: ...

Utilize the $sample operator following the $group stage in MongoDB queries

Consider the dataset provided below: {company:"One", employee:"John"}, {company:"One", employee:"Mike"}, {company:"One", employee:"Donald"}, {company:"One", employee:"Mickey"}, {company:"Two", employee:"Johnny"}, {company:"Two", employee:"Da ...

What purpose does the .set() function serve in Node.js with Express?

As I delve into learning Node syntax, there's this particular code snippet that has caught my curiosity. Can you shed some light on its purpose? server.set('views', __dirname); ...

Issues with XFBML Like Buttons failing to load when generating numerous posts dynamically on a single page

On my webpage containing multiple posts, I am attempting to insert a Facebook LIKE button for each post. Utilizing XFBML code, I am trying to populate like buttons under every individual post with a unique URL, corresponding to the post URL. Here is the c ...

Avoiding redirection in Django template form

Currently, I am facing a challenge with my application that involves rendering a Django Template model form where images are referenced from another model. To manage the addition and deletion of images for this other model, I have implemented a button wit ...

The functionality of AngularJS ng-disable is failing to work on an anchor tag

I am currently facing a challenge in my AngularJS project where I need to disable an icon within an ng-repeat scenario based on a condition. Specifically, I want to check if the owner is null and then disable the icon accordingly. However, despite verifyin ...