Wrap function with promise

Question

Okay, so I've almost got the hang of promises.

I'm trying to figure out how to place a promise within view_functions so that the return works.

function loadViewFunctions(view_functions,append_data){

    var this_app_data = [];

    function viewFunctions(){

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

            this_app_data[i] = window[view_functions[i]]();

        }
        for (i = 0; i < this_app_data.length; i++) {

            this_app_data[i].then(function(this_d) {

                append_data = append_data + this_d;

            });
        }
        return append_data;
    }

    //return
    return viewFunctions().then(post_app_data => {
        return post_app_data;
    });
};

The `then` in the return statement doesn't do anything. Is it meant to be doing something? — PeterMader, Oct 11 '17 at 18:07
@Bergi the function is camelCase while the argument is snake_case, so they don't conflict. But that threw me off for a second too. — Sidney, Oct 11 '17 at 18:08
No Bergi, look closely, one has an underscore, the other does not. — Ryan Christopher, Oct 11 '17 at 18:09
You really should pass an array of functions, not an array of names of global functions — Bergi, Oct 11 '17 at 18:09
They are coming from a JSON object. Therefor they have to be names. — Ryan Christopher, Oct 11 '17 at 18:11
That doesn't mean that the resolution of those names has to happen here. It could be in the calling code. — Scott Sauyet, Oct 11 '17 at 18:12
If you could provide an example of something better that would be awesome... — Ryan Christopher, Oct 11 '17 at 18:14
@PeterMader Yes it does, but that doesn't need to be seen here. — Ryan Christopher, Oct 11 '17 at 18:17
@RyanChristopher If they have to be names, at least don't make them names of global variables but rather names to look up in a `Map` or local object. — Bergi, Oct 11 '17 at 18:20
i don't understand why a very common duplicate needs so much discussion. make an array of promises, wait on them to complete. — Kevin B, Oct 11 '17 at 18:21

score 0 · Accepted Answer · edited Oct 11 '17 at 18:19

0

The following snippet should be equivalent to what I think you are trying to achieve:

function loadViewFunctions (view_functions, initial_append_data) {
  // retrieve the functions and calls them
  const promises = view_functions.map(f => window[f]());
  return Promise.all(promises).then(
    // join the results together
    results => results.reduce((acc, this_d) => acc + this_d), initial_append_data)
  );
}

It uses

map to iterate over an array and create a new one and
Promise.all to wait until all promises that you give to it have resolved

As others have mentioned in the comments, don't use function names to access global functions. Pass an array of functions instead.

edited Oct 11 '17 at 18:19

Bergi

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answered Oct 11 '17 at 18:17

PeterMader

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There is an error in the code. – Ryan Christopher Oct 11 '17 at 18:20
Honestly so confused by this code. – Ryan Christopher Oct 11 '17 at 18:21
You were right, the error has been edited out. What parts of the code do you not understand? – PeterMader Oct 11 '17 at 18:47
still an error lol, and i understand it now... – Ryan Christopher Oct 11 '17 at 18:55
Fixed error... works. Thank you good sir! – Ryan Christopher Oct 11 '17 at 19:09
Good to hear that. I must admit my code is a little too succinct and perhaps hard to understand. – PeterMader Oct 11 '17 at 19:50
You know your stuff. Hard to find people like you. – Ryan Christopher Oct 11 '17 at 20:01

Wrap function with promise

1 Answers1