NodeJS - Get an array from an async for loop

Question

I am fairly new to nodejs coding and ran into a problem where i can't get the items i can log in console into an array for processing from a for each loop which makes a url request.

The code here first gets a list of keys from a request which i then turn into names using another request in the for each loop.

I need to log the name list in an array where it says 'need an array here', here is my current code:

request('https://api2.ripaex.io/api/delegates/getNextForgers', function (error, response, body) {
  if (!error && response.statusCode == 200) {
    var jsonContent = JSON.parse(body);
    var delegates = jsonContent.delegates;
    for (i = 0; i < delegates.length; ++i) {
        request(String('https://api2.ripaex.io/api/delegates/get?publicKey=' + delegates[i]), function (error, response, body) {
          if (!error && response.statusCode == 200) {
            var jsonContent2 = JSON.parse(body);
            console.log(jsonContent2.delegate.username);
          }
        })
    }
    console.log('need an array here');
  } else { console.log('Error: Could not retrieve the data') }
})

request is async function. You can't do that. You should look into promises. developers.google.com/web/fundamentals/primers/promises github.com/request/request-promise-native — Jerinaw
– Jerinaw, Commented Aug 9, 2018 at 0:31

Jerinaw · Accepted Answer · 2018-08-09 14:44:59Z

2

I did not test this, but this is what I was referring to in the comment.

request('https://api2.ripaex.io/api/delegates/getNextForgers', function(error, response, body) {
    if (!error && response.statusCode == 200) {
        var jsonContent = JSON.parse(body);
        var delegates = jsonContent.delegates;
        var promises = [];

        for (i = 0; i < delegates.length; ++i) {
            promises.push(new Promise(function(resolve, reject) {
                request(String('https://api2.ripaex.io/api/delegates/get?publicKey=' + delegates[i]), function(error, response, body) {
                    if (!error && response.statusCode == 200) {
                        var jsonContent2 = JSON.parse(body);
                        console.log(jsonContent2.delegate.username);
                        resolve(jsonContent2);
                    }else{
                        reject(error);
                    }
                })
            }
            ));
        }

        Promise.all(promises).then(function(resultsArray){
            console.log('need an array here');
        }).catch(function(err){
           //Handle errors
        });

    } else {
        console.log('Error: Could not retrieve the data')
    }
});

But here is the request api already wrapped in promises https://github.com/request/request-promise-native

Here's an untested example using the request-promise api.

var rp = require('request-promise');

rp({
    method: 'GET',
    uri: 'https://api2.ripaex.io/api/delegates/getNextForgers',
    json: true // Automatically stringifies the body to JSON
    //resolveWithFullResponse: true //If you want the full response
}).then(function(jsonContent) {
    var delegates = jsonContent.delegates,
        promises = [];

    for (i = 0; i < delegates.length; ++i) {
        promises.push(rp({
            url: String('https://api2.ripaex.io/api/delegates/get?publicKey=' + delegates[i]),
            json: true
        }).then(function(jsonContent2) {
            console.log(jsonContent2.delegate.username);
            return jsonContent2;
        }));
    }

    return Promise.all(promises).then(function(resultsArray) {
        console.log('need an array here');
    });


}).catch(function(err){
    console.log('Error: Could not retrieve the data')
});

edited Aug 9, 2018 at 14:44

answered Aug 9, 2018 at 0:40

Jerinaw

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7 Comments

jfriend00 Over a year ago

My as well just use the request-promise module rather than wrapping your own promise around request. It also has options to parse the JSON for you automatically and checks the status code for you automatically too.

Jerinaw Over a year ago

Yes, I put that in my comment.

jfriend00 Over a year ago

Why not show it in the code of your answer? IMO, it would make for a better answer.

jfriend00 Over a year ago

New to JS is the exact right time to start using request-promise instead of request. Promises over regular callbacks. And, it's better to teach someone the existing module that uses promises rather than duplicating promisifying something that's already been done and in wide use.

jfriend00 Over a year ago

Missing a .catch() handler on the Promise.all() or need to return the Promise.all() promise. No error handling on the promises from the for loop.

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