FileReader.readAsDataURL()

FileReader.readAsDataURL()

HTML

<!-- Learn about this code on MDN: https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL -->

<input type="file" onchange="previewFile()">
<br>
<img id="im" src="" height="200" alt="Image preview...">

JavaScript

function previewFile() { 
  var preview = document.getElementById('im'); 
  var file   = document.querySelector('input[type=file]').files[0]; 
  var reader  = new FileReader();

   
  reader.addEventListener("load", function() {  
    preview.src = reader.result; 
  }, false);

   
  if (file) {  
    reader.readAsDataURL(file); 
  }
}