Display Images in an Image Viewer - HTML5 JavaScript

window.onload = function () { 
  var licenseUrl = "./LEADTOOLS/LEADTOOLS.lic.txt"; 
  var developerKey = "REPLACE_WITH_KEY_CONTENTS"; 
  lt.RasterSupport.setLicenseUri(licenseUrl, developerKey, function ( 
    setLicenseResult 
  ) { 
    // Check the status of the license 
    if (setLicenseResult.result) { 
      console.log("LEADTOOLS client license set successfully"); 
    } else { 
      var msg = "LEADTOOLS License is missing, invalid or expired\nError:\n"; 
      console.log(msg); 
      alert(msg); 
    } 
  }); 
 
  // Create an image viewer inside the imageViewerDiv element 
  const imageViewerDiv = document.getElementById("imageViewerDiv"); 
  const createOptions = new lt.Controls.ImageViewerCreateOptions( 
    imageViewerDiv 
  ); 
  this.imageViewer = new lt.Controls.ImageViewer(createOptions); 
  this.imageViewer.viewVerticalAlignment = lt.Controls.ControlAlignment.center; 
  this.imageViewer.viewHorizontalAlignment = 
    lt.Controls.ControlAlignment.center; 
  this.imageViewer.autoCreateCanvas = true; 
 
  // Add Pan/Zoom interactive mode 
  // Click and drag to pan, CTRL-Click and drag to zoom in and out 
  this.imageViewer.interactiveModes.add( 
    new lt.Controls.ImageViewerPanZoomInteractiveMode() 
  ); 
 
  // Load an image 
  this.imageViewer.imageUrl = 
    "https://demo.leadtools.com/images/jpeg/cannon.jpg"; 
 
  this.imageViewer.zoom( 
    lt.Controls.ControlSizeMode.fit, 
    0.9, 
    this.imageViewer.defaultZoomOrigin 
  ); 
 
  //Input a file 
  const fileInput = document.getElementById("fileInput"); 
  fileInput.addEventListener("change", (event) => { 
    //Change the URL of the viewer image to the input file. 
    if (event.target.files[0] != null) 
      this.imageViewer.imageUrl = URL.createObjectURL(event.target.files[0]); 
  }); 
 
  //Download functionality 
  const downloadButton = document.getElementById("downloadButton"); 
  downloadButton.addEventListener("click", () => { 
    var image = new Image(); 
    image.crossOrigin = "anonymous"; 
    image.src = this.imageViewer.imageUrl; 
 
    document.body.append(image); 
    image.onload = () => { 
      var canvas = document.createElement("canvas"); 
      canvas.width = image.width; 
      canvas.height = image.height; 
      canvas.getContext("2d").drawImage(image, 0, 0); 
 
      var blob; 
      blob = canvas.toDataURL("image/jpeg"); 
 
      var a = document.createElement("a"); 
      a.href = blob; 
      a.download = "output.png"; 
      document.body.appendChild(a); 
      a.click(); 
      document.body.removeChild(a); 
    }; 
    document.body.removeChild(image); 
  }); 
};