JSFiddle - React, Tailwind, and code Playground

JavaScript

$(document).ready(function() {
      $.when(myFunction())
        .done(function(result) {
          // ...
          console.log("all done");
        }).fail(function(err) {
          // ...
        });
    });
    
    function myFunction() {
      return ($.when(someOtherAction())
                .done(function(result) {
                  return (result);
                }).fail(function(err) {
                  // ...
                })
             );
    }
    
    function someOtherAction() {
      // ...
        for (var i = 0; i < 100000000; i++) {
            ;
        }
      return (true);
    }