var remoteImage, 
    container = document.querySelector('.imageContainer'),
    toLoad = { 'images': [ 
       'http://myserver.com/image1.png', 
       'http://myserver.com/image2.png' ] }; // list of image URLs

toLoad.images.forEach(function(imageToLoad) {
      remoteImage = new RAL.RemoteImage(imageToLoad);
      container.appendChild(remoteImage.element);
      RAL.Queue.add(remoteImage);
});
RAL.Queue.setMaxConnections(4);
RAL.Queue.start();
 

function loadImage(uri,callback){
	if(typeof callback!='function'){
		callback=function(uri){
			console.log(uri);
		}
	}
	var xhr = new XMLHttpRequest();
	xhr.responseType = 'blob';
	xhr.onload = function() {
		callback(window.URL.createObjectURL(xhr.response));
	}
	xhr.open('GET', uri, true);
	xhr.send();
}

//使用方法
var imgUrl='http:xxx.jpg';
loadImage(imgUrl,function(URI){
	//Do some thing while image is load
});
 

function loadUrl(uri,callback){
	if(typeof callback!='function'){
		callback=function(uri){
			console.log(uri);
		}
	}
	var xhr = new XMLHttpRequest();
	xhr.responseType = 'text';
	xhr.onload = function() {
		callback(xhr.response);
	}
	xhr.open('GET', uri, true);
	xhr.send();
}

//使用方法
var url = 'http:xxx.do';
loadUrl(url,function(data){
	//Do some thing while image is load
});
 

XMLHttpRequest.responseType:
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/responseType
如："document","json","text","blob"