JavaScript loading progress of an image

Question

Is there a way in JS to get the progress of a loading image while the image is being loaded? I want to use the new Progress tag of HTML5 to show the progress of loading imag

Answer 1

With this, you add 2 new functions on the Image() object:

 Image.prototype.load = function(url){
        var thisImg = this;
        var xmlHTTP = new XMLHttpRequest();
        xmlHTTP.open('GET', url,true);
        xmlHTTP.responseType = 'arraybuffer';
        xmlHTTP.onload = function(e) {
            var blob = new Blob([this.response]);
            thisImg.src = window.URL.createObjectURL(blob);
        };
        xmlHTTP.onprogress = function(e) {
            thisImg.completedPercentage = parseInt((e.loaded / e.total) * 100);
        };
        xmlHTTP.onloadstart = function() {
            thisImg.completedPercentage = 0;
        };
        xmlHTTP.send();
    };

    Image.prototype.completedPercentage = 0;

And here you use the load function and append the image on a div.

var img = new Image();
img.load("url");
document.getElementById("myDiv").appendChild(img);

During the loading state you can check the progress percentage using img.completedPercentage.

Answer 2

for xmlhttpreq v2 check, use:

var xmlHTTP = new XMLHttpRequest();
if ('onprogress' in xmlHTTP) {
 // supported 
} else {
 // isn't supported
}

Answer 3

Just to add to the improvements, I've modified Julian's answer (which in turn modified Sebastian's). I've moved the logic to a function instead of modifying the Image object. This function returns a Promise that resolves with the URL object, which only needs to be inserted as the src attribute of an image tag.

/**
 * Loads an image with progress callback.
 *
 * The `onprogress` callback will be called by XMLHttpRequest's onprogress
 * event, and will receive the loading progress ratio as an whole number.
 * However, if it's not possible to compute the progress ratio, `onprogress`
 * will be called only once passing -1 as progress value. This is useful to,
 * for example, change the progress animation to an undefined animation.
 *
 * @param  {string}   imageUrl   The image to load
 * @param  {Function} onprogress
 * @return {Promise}
 */
function loadImage(imageUrl, onprogress) {
  return new Promise((resolve, reject) => {
    var xhr = new XMLHttpRequest();
    var notifiedNotComputable = false;

    xhr.open('GET', imageUrl, true);
    xhr.responseType = 'arraybuffer';

    xhr.onprogress = function(ev) {
      if (ev.lengthComputable) {
        onprogress(parseInt((ev.loaded / ev.total) * 100));
      } else {
        if (!notifiedNotComputable) {
          notifiedNotComputable = true;
          onprogress(-1);
        }
      }
    }

    xhr.onloadend = function() {
      if (!xhr.status.toString().match(/^2/)) {
        reject(xhr);
      } else {
        if (!notifiedNotComputable) {
          onprogress(100);
        }

        var options = {}
        var headers = xhr.getAllResponseHeaders();
        var m = headers.match(/^Content-Type\:\s*(.*?)$/mi);

        if (m && m[1]) {
          options.type = m[1];
        }

        var blob = new Blob([this.response], options);

        resolve(window.URL.createObjectURL(blob));
      }
    }

    xhr.send();
  });
}

/*****************
 * Example usage
 */

var imgContainer = document.getElementById('imgcont');
var progressBar = document.getElementById('progress');
var imageUrl = 'https://placekitten.com/g/2000/2000';

loadImage(imageUrl, (ratio) => {
  if (ratio == -1) {
    // Ratio not computable. Let's make this bar an undefined one.
    // Remember that since ratio isn't computable, calling this function
    // makes no further sense, so it won't be called again.
    progressBar.removeAttribute('value');
  } else {
    // We have progress ratio; update the bar.
    progressBar.value = ratio;
  }
})
.then(imgSrc => {
  // Loading successfuly complete; set the image and probably do other stuff.
  imgContainer.src = imgSrc;
}, xhr => {
  // An error occured. We have the XHR object to see what happened.
});

<progress id="progress" value="0" max="100" style="width: 100%;"></progress>

<img id="imgcont" />

Answer 4

Here is a small update of the code of Julian Jensen in order to be able to draw the image in a Canvas after it is loaded :

xmlHTTP.onload = function( e ) {
        var h = xmlHTTP.getAllResponseHeaders(),
            m = h.match( /^Content-Type\:\s*(.*?)$/mi ),
            mimeType = m[ 1 ] || 'image/png';
            // Remove your progress bar or whatever here. Load is done.

        var blob = new Blob( [ this.response ], { type: mimeType } );
        thisImg.src = window.URL.createObjectURL( blob );

         thisImg.onload = function()
            {
                if ( callback ) callback( this );
            };
    };

Answer 5

Actually, in latest chrome you can use it.

$progress = document.querySelector('#progress');

var url = 'https://placekitten.com/g/2000/2000';

var request = new XMLHttpRequest();
request.onprogress = onProgress;
request.onload = onComplete;
request.onerror = onError;

function onProgress(event) {
  if (!event.lengthComputable) {
    return;
  }
  var loaded = event.loaded;
  var total = event.total;
  var progress = (loaded / total).toFixed(2);

  $progress.textContent = 'Loading... ' + parseInt(progress * 100) + ' %';

  console.log(progress);
}

function onComplete(event) {
  var $img = document.createElement('img');
  $img.setAttribute('src', url);
  $progress.appendChild($img);
  console.log('complete', url);
}

function onError(event) {
  console.log('error');
}


$progress.addEventListener('click', function() {
  request.open('GET', url, true);
  request.overrideMimeType('text/plain; charset=x-user-defined');
  request.send(null);
});

<div id="progress">Click me to load</div>

Answer 6

If you want to process your loaded image, than you have to add one more function, because

thisImg.src = window.URL.createObjectURL(blob)

just starts to process the image as a thread.

You have to add a new a function to the body of load prototype, like

  this.onload = function(e)
  {
    var canvas = document.createElement('canvas')

    canvas.width = this.width
    canvas.height = this.height

    canvas.getContext('2d').drawImage(this, 0, 0)
   }

This make me headache to realize :)