adobe proposal:
http://blogs.adobe.com/webplatform/2012/01/13/html5-image-progress-events/
workaround:
function loadImage(imageUrl, onprogress) {
return new Promise(function(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();
});
}
