Quick Image Validator for checking the quality of images

imageValidator.js

// imageValidator.js

'use-strict';

function handleFileSelect(evt) {
    let files = evt.target.files; // FileList object

    // Loop through the FileList and render image files as thumbnails.
    for (let i = 0; i < files.length; i++) {

      // Only process image files.
      if (!files[i].type.match('jpeg|bmp|png')) {
        alert('Jak je psáno, podporuje jen soubory BMP, JPG nebo PNG!\nSoubor: ' + files[i].name + 'je typu ' + files[i].type + '.');
      } // end IF testing of the file type
      
      // Create new Filereader object, do not create the object in the case the files[i] does not match the proper file type!
      if (files[i].type.match('jpeg|bmp|png')) {
          
          let reader = new FileReader();
    
          // Closure to capture the file information
          reader.onload = (function(theFile) {
            
            return function(e) {
            
              // Creating the enclosing div
              let item = document.createElement('div');
    
              // Create new Image object
              let image = new Image();
              
              // Assign the Image object’s onload logic, everything happens here
              image.onload = function() {
              	let widthDPI300 = image.width / 300 * 2.54;
                let heightDPI300 = image.height / 300 * 2.54;
    
                // Create elements, use Image object’s properties
                item.className    = widthDPI300 < 5 | heightDPI300 < 5 ? 'alert alert-danger tight' : 'alert alert-success tight';
                let img           = document.createElement('img');
                    img.className = 'thumb';
                    img.src       = e.target.result;
                    img.title     = escape(theFile.name)
                let infoPars      = document.createElement('p');
                    infoPars.innerHTML = '<p>název: ' + theFile.name + '<br/>rozměry (px): ' + image.width + ' × ' + image.height + '<br/>rozměry (cm): <b>' + widthDPI300.toFixed(2) + ' × ' + heightDPI300.toFixed(2) + '</b></p>';
                    // Appending the information
                    item.appendChild(img);
                    item.appendChild(infoPars);
    
                document.getElementById('image-list').insertBefore(item, null);      
              } // END image.onload
              
              // Load the image
              image.src = this.result;                    
              
            } // END the function;
          })(files[i]);

      // Read in the image file as a data URL
      reader.readAsDataURL(files[i]);
      
      } // END the Filereader object creation
    } // END processing the whole batch
  } // END the main function
  
// CLEAN THE RESULTS
function cleanResults() {
     
  let results = document.getElementById('image-list');
  let input   = document.getElementById('files');
  
  // Cleaning the list of the results
  while (results.firstChild) {
    results.removeChild(results.firstChild);
  }
  // Cleaning the input
  input.value = '';
      
}

// Assigning event listeners
document.getElementById('files').addEventListener('change', handleFileSelect, false);
document.getElementById('clean-list').addEventListener('click', cleanResults, false);