The goal of Wan is to reduce http overhead by cutting requests to static resources,
without requiring you to make any significant changes to your current sites. Wan will radically affect
your site's request footprint. Click to see a video side-by-side comparisson of a website with and without
Currently, the only feature implemented is data URI spriting, which lets you stream all of your site's static images to a client in a single HTTP request, without having to maintain a sprite-sheet.
Wan is a two part library, containing a single file for the client, and a node module for the server, available currently as a piece of Koa or Express middleware.
Wan is available for node.js via npm
npm install wan
The client library exposes a single function,
Wan, which you use to set options. You call
to request the image stream from your server.
; //returns Wan againWan;
Where options may contain any of the following:
true): Enables caching requests in memory on the client side
true): Enables persistent caching in Local Storage
"wan-cache-"): Prefixes all keys stored in Local Storage
"wan-expires"): Local Storage key which contains cache expiration info
"/wan"): The route which is
GETrequested from your server for Wan
Allows you to get all images on a page with a single xmlHttpRequest, by calling
img tag in the DOM when
getImages is called that has a
data-src attribute will be
added to the request, and have its
src set to a data URI as soon as it has been send to the client.
The response is chunked and evaluated on every progress update in order to display images as soon as
possible, without needing to wait for the response to finish.
The example above will make a single request to your server, pulling
f.png is unaffected because it does not have a
data-src attribute. Once an image has
been loaded with Wan, it loses its
data-src attribute for a
diskCache is enabled, then the client will check Local Storage for the file before requestng it
from the server. A response with a
Cache-Control: max-age or
Expires header will store a special value
in local storage that will serve to invalidate the Local Storage cache appropriately.
You can control the order that your images load by adding the
priority attribute to your
Priorities should be integers. Images with lower priorities load before images with higher priorities.
Images without priorities are loaded after images with priorities. If image priorities are equal, then
their order in the DOM is compared, loading images that appear higher in the DOM first.
<!-- Loads second--><!-- Loads last (no priority given) --><!-- Loads third --><!-- Loads first -->
'wan/koa' will give you middleware that you can use with Koa. Requiring
'wan/express will give you express middleware.
var wan = ;app;
Where options contains the following:
"100MB"): Limits the size of the image cache in RAM
Wan employs data URIs, local cache, and the idea behind CSS spriting to reduce the number of requests a page needs to make to get images. When
getImages is called, a request is made to your server that contains the paths of all the images on the page with a
data-src attribute. This is sent as a query string (if the URL is under 2000 characters), or the body of a POST request.
On the server, the file paths are parsed out. Files are openned (or retrieved from the server's cache) and streamed one by one, base64 encoded, into the server response.
On the client, the response is parsed as it streams in, setting the
src attribute of each image requested as soon as the data has come through. The result is a single, streamed process, which prevents any unecessary waiting for entire processess to finish before the next begins.