jQuery - Maintain Order of .each() while using .getJSON

Question

I have a working function that checks for any input with a specific class name, then runs a getJSON call for each input's value:

function getTopFeeds() {
  if (jQuery('input.class-name').length > 0) {
    jQuery.each(jQuery('input.class-name'),function(){
      var feedName = jQuery(this).val();
      jQuery.getJSON("https://api.url/"+feedName).success(function(data) {
        if (!(data)) {
           return;
        }
        var result = data.results[0];
        if (result) {
            // Here I create HTML list items to display API data
        }
      });
    });
  }
}

It works, but because it's asynchronous it's not returning in the order the inputs on the page. How can I modify my existing function so that the data is displayed in the same order of the inputs?

Answer 1

If you want to wait until they've all come back, you can keep the results in an array and remember how many results you've seen; when you've seen as many results as requests, you're done. See comments:

function getTopFeeds() {
    if (jQuery('input.class-name').length > 0) {
        // Get the inputs
        var inputs = jQuery('input.class-name');
        // Storage for the results
        var results = [];
        // Counter for # of responses we've seen
        var counter = 0;
        // Get them
        inputs.each(function(index) {
            var feedName = this.value;
            jQuery.getJSON("https://api.url/" + feedName)
                .done(function(data) {
                    // Got a response, save it or null if falsy (would that really happen?)
                    results[index] = data ? data.results[0] : null;
                })
                .fail(function() {
                    // Error response, use null as a flag
                    results[index] = null;
                })
                .always(function() {
                    // Called after `done` and `fail` -- see if we're done
                    if (++counter === inputs.length) {
                        // Yes, we're done -- use the results in `results`
                        // Note that there will be `null`s for any that
                        // didn't have data
                    }
                });
        });
    }
}