Calling an asynchronous function from a functional map in JavaScript, how?

Question

JavaScript

There is an array of objects. I would like to map for it by making an HTTP request for each object and returning a new response object.
How to do this if the http module from Node.js is used for HTTP requests, which makes the call asynchronously?

Answer 1

If you master the article, the question will disappear blog.jcoglan.com/2013/03/30/callbacks-are-imperative-promises-are-functional-nodes-biggest-missed-opportunity/

Answer 2

The async module is here to help. Namely, the map method .

Answer 3

You can do it like this: github.com/caolan/async#eachseriesarr-iterator-callback

Answer 4

It doesn't look like it looks like this:

inObjs.map(function /*ААА*/ (o) {
  var req = http.request(options, function (res) {
    var data = "";
    res.on('data', function (chunk) { data += chunk; };
    res.on('end', function () { /* Теперь надо объект data вернуть из лямбда-функции ААА */ ??? });
  });
  res.write(JSON.stringify(o));
  res.end();

  return /* Здесь надо дождаться того объекта data и вернуть его обратно в map */ ???
});

And the parallelism or seriality of the operation of map or eachSeries does not play a role here.

Answer 5

Here's what happened in the end:

/**
 * Event-style map function with fun(e, consumer) as an element
 * transformation function that does not return modified object
 * but produce it to the ''consumer'' function instead.
 *
 * Result of the evmap-transformed objects will be transfered in
 * the ''callback'' call eventually.
 *
 * Main use is for maps with asynchronous transformation functions!
 */
function evmap(list, fun, callback) {
    function evmap(acc, list, fun) {
        if (list && 0 < list.length) {
            fun(list.shift(),
                function (result) {
                    acc.unshift(result);
                    evmap(acc, list, fun);
                });
        }
        else {
            callback(acc.reverse());
        }
    }
    evmap([], list, fun);
}

//// unit tests
exports.evmap_array = {
    'list': function (test) {
        evmap([1,2,3],
              function (e, c) { c(e + 10); },
              function (result) {
                  test.deepEqual(result, [11, 12, 13]);
                  test.done();
              });
    }
};