How can I call a function only once all requests have finished?

Question

I am currently generating a few requests using the npm package request like this:

for (var i = 0; i < array.length; i++) {

    var options = {
        url: '...',
        headers: {
            '...'
        }
    };
    function callback(error, response, body) {

    };
    request(options, callback);

}


function toBeCalledWhenAllRequestsHaveFinished() {

}

I just don't know how to call toBeCalledWhenAllRequestsHaveFinished() only once all requests have finished.

What should be done ?

Alternate - use `Promise.all`. It gives success when all of your requests have completed — Aseem Upadhyay, Jun 28 '18 at 13:08
Have a look at https://davidwalsh.name/promises, it's from 2015 but still a pretty good source to understand promises — Sebastiaan van Arkens, Jun 28 '18 at 13:10
Using this `request` interface module, following this [`GitHub`](https://github.com/request/request-promise-native) link. — Alex, Jun 28 '18 at 13:10

Alex · Accepted Answer · 2018-06-28T14:20:05.973

1

I would highly recommend using node-fetch package.

Reference to the original poster

Install node-fetch using npm install node-fetch --save.

Make a promise-returning fetch that resolves to JSON

const fetch = require('node-fetch');
function fetchJSON(url) {
    // Add options
    var options = {
        headers: {
            '...'
        }
    };
    return fetch(url, options).then(response => response.json());
}

Build an array of promises from an array of URLs

let urls = [url1, url2, url3, url4];
let promises = urls.map(url => fetchJSON(url));

Call toBeCalledWhenAllRequestsHaveFinished() when all promises are resolved.

Promise.all(promises).then(responses => toBeCalledWhenAllRequestsHaveFinished(responses));

edited Jun 28 '18 at 14:20

answered Jun 28 '18 at 13:20

Alex

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If you have to duplicate a whole answer, then you should rather close this question as a duplicate. – str Jun 28 '18 at 13:27
The answer in the post was not marked as `Best Answer`, so until then, there is no point flagging this. – Alex Jun 28 '18 at 13:28
That doesn't matter. It is the most upvoted question at least. – str Jun 28 '18 at 13:29
It is, if you want to flag this post, I will not stop you. – Alex Jun 28 '18 at 13:30
What about the options ? – TheProgrammer Jun 28 '18 at 14:09
@TheProgrammer check the updated code. You should read documentation too. – Alex Jun 28 '18 at 14:15
@TheProgrammer also go to `node-fetch` npm webiste, `Ctrl`+`F` and search for `fetch(url[, options])`. – Alex Jun 28 '18 at 14:18
@Alex I am getting `{"size":0,"timeout":0}` as a response – TheProgrammer Jun 28 '18 at 15:19
I'm pretty sure the options need to be wrapped somehow, I've never used `node-fetch`, check the documentation and try follow what it says. – Alex Jun 28 '18 at 15:20
@Alex I can't accept an incomplete answer per SO rules – TheProgrammer Jun 28 '18 at 15:21
I presume you need to wrap your options in `{}` such as ` return fetch(url, {options})` – Alex Jun 28 '18 at 15:21
@TheProgrammer I'm not focused on the `Accepted Answer`, I'm focused on getting your code to work. – Alex Jun 28 '18 at 15:22
@TheProgrammer search for `// post with JSON` on [`bitinn/node-fetch github`](https://github.com/bitinn/node-fetch). It shows you how to add headers and other options. – Alex Jun 28 '18 at 15:24
@Alex If I do that, the response works, but I need to be able to modfiy the data that is sent back in each response, I am currently trying: }).then(function(response) { console.log("RESPONSE: "+JSON.stringify(response)); but it fails – TheProgrammer Jun 28 '18 at 15:48
@Alex Edited question. – TheProgrammer Jun 28 '18 at 15:49
@TheProgrammer have you added `responses` argument in your `toBeCalledWhenAllRequestsHaveFinished()` function. Add it and inside that function do `console.log(responses)` – Alex Jun 28 '18 at 15:50
@Alex Edited my question with full pseudocode now so you get a better picture of what I want to do. (Still got the same response after adding what you suggested) – TheProgrammer Jun 28 '18 at 16:01
@str Would you know what is happening here ? – TheProgrammer Jun 28 '18 at 16:06
1

Ultimately found the solution. You pointed me in the right direction. Answer accepted and upvoted :D Have a great day ! – TheProgrammer Jun 28 '18 at 19:06
That's great to hear. Happy to be any help! :) @TheProgrammer – Alex Jun 28 '18 at 19:14

How can I call a function only once all requests have finished?

1 Answers1