Chain of endpoints in Node and Express: how to prevent that some of them stops all the series?

Question

In some page I have to get information from 8 different endpoints. 2 of them are outside of my application and sometimes they cause an delay at displaying data. The web browser waits until the data is processed. Once they're outside of my app I can't refactor them in order to make them fast, but I need to show the information that they provide. In addition, sometimes one of them returns nothing. If so, I use default data to show to the user. The waiting time takes time for the user experience perspective.

I'm using promises to call these endpoints. Below is part of the code snippet that I am using.

The code is working fine. The issue is the delay.

First. Here is the array that contains all the service that I need to process:

        var requests = [{
            // 0
            url: urlLocalApi + '/endpointURL_1/',
            headers: {
                'headers': 'apitoken'
            },
        }, {
            // 1
            url: urlLocalApi + '/endpointURL_2/',
            headers: {
                'headers': 'apitoken'
            },
        ];

The code of array is encapsulated in this method:

    const requests = homePageFunctions.createRequest();

Now, it is how the data is processed. I am using both 'request-promise' and 'bluebird', and a personal logger to check it out if everything goes fine.

const Promise = require("bluebird");
const request = require('request-promise');

var viewsHelper = {
    getPageData: function (requests) {
        return Promise.map(requests, function (obj) {
            return request(obj).then(function (body) {
                AppLogger.log(`Endpoint parsed`, statusLogger.infodate);
                return JSON.parse(body);
            });
        });
    }
}

module.exports = viewsHelper;

How do I call this?

    viewsHelper.getPageData(requests)
        .then(results => {
            var output = [];
            for (var i = 0; i < results.length; i++) {
                output.push(results[i]);
            }

            // render data
            res.render('homepage/index', output);
            AppLogger.log(`PageData is rendered`, statusLogger.infodate);
        })
        .catch(err => {
            console.log(err);
        });
};

Take a look that inside of each index item of "output" array, there is the output of each data of each endpoint.

The problem here is:

If any of the endpoint takes long, the entire chain slows even though if they are already processed. The web page waits in a blank mode.

How to prevent this behavior?

Answer 1

That is an interesting question but I have questions in order to answer it effectively.

You have Node server and client (HTML/JS)

You have 8 end points 2 are slow because you don’t have control over them.

1. Does the client (page) aware of the 8 end points? I .e you make 8 calls everytime you reload the page?

OR

2. Does the page makes one request to your node JS and your nodeJS synchronously calls the 8 end points

If it is 1 then lazy loading will work easily for you since the page is making the requests.

If it is 2 lazy loading will work only at the server side however the client will be blocked because it doesn’t know (or care how you load your data. The page made one request and it is blocked waiting for that request..

Obviously each method has pros and cons ..

One way you can solve this is to asynchronously call those end points on node and cache them and when the page makes the 1 request you have the data ready ..

Again we know very little about the situation there are many ways to solve this

Hope this helps