Abusing Javascript to speedup mobile web sites

Abusing Javascript to speedup mobile web sites.

Mobile browsers are dog slow

Only if they are used to render web sites designed for desktop browsers.

One code for any browser and device is actually a dream.

Bad code tends to have more impact on mobile browsers.

Radio networks are slow

The main issue is not speed but latency.

4 Mb downloaded over a single request: 2 seconds.

Same data downloaded as 20 small files: 8 seconds.

A 304 reply code is nearly as bad as a 200

404 replies are rarely cached. Kill them all.

Proper caching of anything cacheable is required

Don't overestimate the browser cache and HTTP keep-alive.

HTML5 cache manifest

Doesn't bring much over proper HTTP caching for online apps.

Everything in the manifest is preloaded even when useless for the current page. Double-sided sword.

Requests from a cached page have no referrer.

No granularity: everything depends on the freshness of the manifest.

Mobile browsers have unpredicable caching

strategy

Even on the same operating system

iOS 4.1 on iPhone 3G doesn't cache some tiny content that could really be cached. And that the same OS on other devices does.

JavaScript to the rescue!

Slower may feel faster

Mobile devices have small screens.

Load visible content first, and use XHR to load the rest.

Don't wait until the user scrolls, though. Latency + tendency to scroll and zoom on mobile devices would make the page feel slow.

Provide feedback.

JS + HTTP caching = not so bad

Don't repeat yourself: use static JS to render common, static fragments.

Use XHR to render dynamic parts that are not immediately visible.

Different parts can have different expiration.

HTTP cache is quite unpredictable

No control over actual eviction.

Might feel good, even for large requests, until everything is evicted.

The server controls the cache, not the client (which could come in handy to avoid inconsistencies).

Localstorage is the real shit

Seamlessly keeps over 2.5 Mb of data per domain.

Mostly persistent.

Provides a flexible client-controlled cache for any resource.

Trivial to implement.

if (window.localStorage["geoapi_js-v5"]) { window.eval(window.localStorage["geoapi_js-v5"]);} else { var xhr = new XMLHttpRequest; xhr.onreadystatechange = function() { if (this.readyState != 4) { return; } if (this.status != 200) { alert("Erreur reseau: " + this.status); return; } try { window.localStorage["geoapi_js-v5"] = this.responseText; } catch (e) { } window.eval(this.responseText); }; xhr.open("GET", "geoapi-v5.js", true); xhr.send();}

Client-side fragment caching

Dramatically improves performance of a non-AJAXified page with minor changes.

Use localstorage to store common fragments.

Tell the server about known fragments so that only identifiers from the previous page are sent, in place of the actual content.

<!doctype html><html><head> <title>Transparent client-side fragment cache demo</title></head><body> <nav> Navigation bar </nav> <div id="ads"> Ads </div> <section id="hey"> I ain't no <a href="/">fragment</a>! </section> <script src="disco.js"></script></body></html>

<section id="hey"> I ain't no <a href="/">fragment</a>! </section>

gets dynamically rewritten as:

<section id="hey"> I ain't no <a href="/?_fragments=navbar-290d996311209f1897516b2caa2cc611+ads-bd779001f9cad4bfb74e563eb6bbf5c5">fragment</a>! </section>

<!doctype html><html><head> <title>Transparent client-side fragment cache demo</title></head><body> <section id="hey"> I ain't no <a href="/">fragment</a>! </section> <script src="disco.js"></script></body></html>

http://00f.net/2010/09/22/transparent-client-side-

fragment-cache/

Frank@jedisct1

Abusing Javascript to speedup mobile web sites

Technology

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