How do I return the accumulated results of multiple (parallel) asynchronous function calls in a loop?

Question

I have a function foo which makes multiple (parallel) asynchronous calls in a loop. I need to somehow wait until the results of all of the calls are available.

Answer 1

A simple way of doing it would be to trigger a callback once all responses are in the array:

function foo(cb) {
    var results = [];

    for (var i = 0; i < 10; i++) {
      someAsyncFunction({someParam:i}, function callback(data) {
        results.push(data);

        if(results.length===10){
          cb(results);
        }
      });
    }

}

foo(function(resultArr){
    // do whatever with array of results
});

Only difference from the Promise.all approach is the order of the results is not guaranteed; but that is easily achievable with a few additions.