JSFiddle - React, Tailwind, and code Playground

HTML

<input id='file-dlg' type='file'/>
    <br/>
    <button id='submit' type='button'>submit</button>

JavaScript

document.getElementById('file-dlg').addEventListener('change', storeAPromise);
     var p; 
     function storeAPromise() {
       p = new Promise(function executor(resolve, reject) {
         try {
           throw new Error('snafu');
         } catch(e) {
           reject(e);
         }
       });
     };
     document.getElementById('submit').onclick = function() {
       p.then(function() {}, function reject(e) {
         console.error('some problem happenned', e);
       });
     };