Работа с файлом, полученным из input “file” [закрыт]

function onFileLoad(elementId, event) { 
  document.getElementById(elementId).innerText = event.target.result; 
} 
 
function onChooseFile(event, onLoadFileHandler) { 
  if (typeof window.FileReader !== 'function') 
    throw ("The file API isn't supported on this browser."); 
  let input = event.target; 
  if (!input) 
    throw ("The browser does not properly implement the event object"); 
  if (!input.files) 
    throw ("This browser does not support the `files` property of the file input."); 
  if (!input.files[0]) 
    return undefined; 
  let file = input.files[0]; 
  let fr = new FileReader(); 
  fr.onload = onLoadFileHandler; 
  fr.readAsText(file); 
}

<input type='file' onchange='onChooseFile(event, onFileLoad.bind(this, "contents"))' /> 
<br> 
<div style="background: #e9e9e9"> 
  <code id="contents"></code> 
</div>