High-Performance Java. Script: Why Everything You’ve Been Taught is Wrong Joseph Smarr Plaxo, Inc.
About me - Chief Platform Architect at Plaxo - - First employee (March 2002) Architect and lead developer for Plaxo Online Abusing web browsers since 1993 (Mosaic) - Plaxo Online 2. 0 (AJAX via iframes in 2004) - Java. Script Wormhole (OSCON 06) http: //Joseph. Smarr. com Joseph Smarr, Plaxo, Inc.
About Plaxo - Smart Address Book - - Syncs address book and calendar with lots of places User updates their contact info you get it automatically Founded in 2002, ~50 employees, 15 M+ users - Backed by Sequoia, Ram Shriram, Tim Koogle, et al http: //www. plaxo. com Joseph Smarr, Plaxo, Inc.
Plaxo Online AJAX Desktop beta. plaxo. com • Flexible desktop • Contacts • Calendar • Tasks • Notes • Sync dashboard • Pulse • Profile / settings Joseph Smarr, Plaxo, Inc.
Plaxo Online AJAX Desktop beta. plaxo. com • Flexible desktop • Contacts • Calendar • Tasks • Notes • Sync dashboard • Pulse • Profile / settings Joseph Smarr, Plaxo, Inc.
Plaxo Online AJAX Desktop beta. plaxo. com • Flexible desktop • Contacts • Calendar • Tasks • Notes • Sync dashboard • Pulse • Profile / settings Joseph Smarr, Plaxo, Inc.
Looks great…but it almost didn’t ship! - Spring 06: “Let’s really push the envelope for Plaxo 3. 0” - Summer 06: “Wow, these are great UI ideas, keep em coming” - Fall 06: “Let’s put 7 great web devs full time on this”’ - Winter 06: “Ok, we built a ton…now let’s optimize it, no problem” - March 07: “Uh oh, making it fast is way harder than we thought” - April 07: “We can’t ship this as is—do we need to start over? !? ” - June 07: “After a heroic effort, it’s just barely fast enough (phew!)” Joseph Smarr, Plaxo, Inc.
Where did we go wrong? ? - Didn’t take performance seriously from day one - Didn’t think the browser’s limitations were significant - Didn’t use the app daily as we were developing it - Didn’t push back on feature requests for performance - Didn’t value perceived performance / responsiveness …overcoming these challenges required unlearning a lot of standard assumptions about building software… Joseph Smarr, Plaxo, Inc.
Why Everything You’ve Been Taught is Wrong - AJAX euphoria - - Web browsers can be made to do anything now! Use desktop / OOP programming style Why it’s wrong - Browsers are being pushed beyond their comfort zone - Java. Script code is parsed & interpreted every time cost per line of source code Joseph Smarr, Plaxo, Inc.
Why High-Performance Java. Script Matters - Everyone is amazed by fast apps - - Everyone hates slow apps - - It hardly matters what else they do! It hardly matters what else they do… AJAX was supposed to be all about responsiveness!! Having tried and almost failed, we now have a mantra: Joseph Smarr, Plaxo, Inc.
The High-Performance JS Mantra - Be Lazy - Be Responsive - Be Pragmatic - Be Vigilant Joseph Smarr, Plaxo, Inc.
The High-Performance JS Mantra - Be Lazy: Nothing is faster than doing nothing - Be Responsive - Be Pragmatic - Be Vigilant Joseph Smarr, Plaxo, Inc.
Write less code - Be Lazy: Nothing is faster than doing nothing Initial parsing of Java. Script is often a major bottleneck - - No JIT, no cached object code, interpreted every time Parse time is non-linear in the size of total Java. Script? Can’t rely on browser caching to excuse large code size - - Yahoo study: surprising number of hits with empty cache Frequent code releases frequently need to re-download More code = more to download, execute, maintain, etc. - Ideal for large AJAX apps is <500 K JS uncompressed Joseph Smarr, Plaxo, Inc.
Total code size of some AJAX apps Joseph Smarr, Plaxo, Inc.
Write less code - Be Lazy: Nothing is faster than doing nothing Minimize the Java. Script code you send down - Minify = good, obfuscate = not much better - Strip debug / logging lines (don’t just set log-level = 0) - Remove unnecessary OOP boilerplate - - Get/Set functions don’t actually protect member vars! etc. Minimize dependency on third-party library code - Lots of extra code comes along that you don’t need - Libraries solve more general problems use like scaffolding Joseph Smarr, Plaxo, Inc.
Be Lazy: Nothing is faster than doing nothing Load Java. Script on-demand - Once you’ve written less code, load it only as-needed “I work hard at - - being lazy” Break into classes / modules; use require / provide (ala dojo) Bundle classes into packages to minimize server round-trips - - Packages should ignore pre-loaded dependencies Tradeoff of downloading shared code twice vs. multiple round trips (e. g. for common widgets) Build packages with error-handler hook for development - Will re-build from source every time if you don’t write Ryan “Roger” Moore Joseph Smarr, Plaxo, Inc.
Be Lazy: Nothing is faster than doing nothing Draw UI as late as possible - Draw less DOM = faster to draw, browser less saturated - Never pre-draw hidden UI if you can avoid it - Cache previously drawn HTML when appropriate - - Don’t keep hidden UI up-to-date behind the scenes - - But have to know when to invalidate the cache Just re-draw next time you show it (simpler, one-time cost) Consider re-drawing vs. partial dynamic UI updates - Redraw is often faster / easier / less code Joseph Smarr, Plaxo, Inc.
Never pre-draw hidden UI Joseph Smarr, Plaxo, Inc.
Never pre-draw hidden UI Joseph Smarr, Plaxo, Inc.
Never pre-draw hidden UI Joseph Smarr, Plaxo, Inc.
Never pre-draw hidden UI Joseph Smarr, Plaxo, Inc.
Never pre-draw hidden UI Joseph Smarr, Plaxo, Inc.
How to Be Lazy √ Write less code! √ Load JS on-demand √ Draw UI as late as possible Joseph Smarr, Plaxo, Inc. Be Lazy: Nothing is faster than doing nothing
The High-Performance JS Mantra - Be Lazy - Be Responsive: Jump when the user says jump - Be Pragmatic - Be Vigilant Joseph Smarr, Plaxo, Inc.
Be Responsive: Jump when the user says jump Minimize initial perceived load time - Put CSS at the top of your page and JS at the bottom - Draw major placeholder UI with “loading…” first - Load / draw your app in stages (lazy, on-demand) Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Load your app in stages Joseph Smarr, Plaxo, Inc.
Be Responsive: Jump when the user says jump Yield early and often - Always want to show a quick response acknowledgement - - But browser often doesn’t update UI until your code returns! Solution: do minimum work, use set. Timeout(0) to yield - Use closures to chain state together with periodic pauses - Draw UI progressively, with loading messages as needed - Use onmousedown instead of onclick (~100 msec faster!) - Demo: http: //josephsmarr. com/oscon-js/yield. html Joseph Smarr, Plaxo, Inc.
Be Responsive: Jump when the user says jump Cache backend responses and “Data structures - AJAX—together at last!” All data requests should go through data-manager code - - Request as needed and cache results for subsequent asks Requesting code always assumes async response Use range caches only fill in missing pieces - - Ideal for partial views into long lists of data Balance local updates vs. re-fetching from APIs Glenn “Fiddich” Dixon - Do the easy cases, but beware of too much update code - Worst case = trash cache and re-fetch = first-time case Joseph Smarr, Plaxo, Inc.
Be Responsive: Jump when the user says jump How to Be Responsive √ Minimize initial perceived loading time √ Yield early and often for responsive UI √ Cache API responses with data-manager layer Joseph Smarr, Plaxo, Inc.
The High-Performance JS Mantra - Be Lazy - Be Responsive - Be Pragmatic: Don’t make things even harder - Be Vigilant Joseph Smarr, Plaxo, Inc.
Be Pragmatic: Don’t make things even harder Play to the browser’s strengths - Avoid DOM manipulation; use inner. HTML and array. join(“”) - Avoid dynamic CSS-class definitions & CSS math - Avoid reflow when possible (esp. manually on browser resize) - Avoid memory allocation (e. g. string-splitting) - Do DOM manipulation off-DOM, then re-insert at the end Joseph Smarr, Plaxo, Inc.
Be Pragmatic: Don’t make things even harder Cheat when you can / should - Use global functions or IDs when reasonable - Finding by class / attaching event handlers is slow - Protect modularity only when needed (e. g. widgets) - Directly attach onclick, etc. handlers instead of using event listeners where appropriate - Use fastest find-elems available when you need to scan the DOM (don’t rely on general-purpose code) Joseph Smarr, Plaxo, Inc.
Be Pragmatic: Don’t make things even harder Inline initial API calls & HTML - Tempting to load blank page and do everything in Java. Script - - Problem: initial load is usually too slow - - Have to redraw UI dynamically; don’t want two copies of UI code Too many round-trips to the server; too long before initial UI shows up Solution: if you have to do it every time, do it statically - Save out initial API responses in web page - Use data-manager to hide pre-fetching (can change your mind later) - Download initial HTML in web page Joseph Smarr, Plaxo, Inc.
Be Pragmatic: Don’t make things even harder How to Be Pragmatic √ Play to the browser’s strengths √ Cheat when you can / should √ Inline initial API calls / HTML for faster load time Joseph Smarr, Plaxo, Inc.
The High-Performance JS Mantra - Be Lazy - Be Responsive - Be Pragmatic - Be Vigilant: Only you can prevent slow web apps Joseph Smarr, Plaxo, Inc.
Profile like crazy - Be Vigilant: Only you can prevent slow web apps Bottlenecks abound are usually not obvious - Use timestamp diffs and alerts - - Use firebug’s profiler (Joe Hewitt, you rule! ) Comment-out blocks of code Measure with a consistent environment - Browsers bog down always restart first - Try multiple runs and average (and don’t forget the cache) Joseph Smarr, Plaxo, Inc.
Firebug is your friend Joseph Smarr, Plaxo, Inc.
Be Vigilant: Only you can prevent slow web apps Consider performance from day one - Apps get slow when you make them do many / slow things! - Consider how much code / work is needed for each feature - - Is it making the browser work against the grain? What else is suffering for this feature? Is it worth it? Make sure everyone remembers how important speed is Joseph Smarr, Plaxo, Inc.
Be Vigilant: Only you can prevent slow web apps Get your priorities straight - Building high-performance apps requires the right attitude - - Must consider and prioritize speed in every decision Ask “what features can I add within this size / speed? ” vs. “how small / fast can I get this set of features? ” - I had to learn this the hard way (Plaxo 3. 0 almost didn’t ship!) “Performance first, features second!” Todd & Cam Joseph Smarr, Plaxo, Inc.
Be Vigilant: Only you can prevent slow web apps How to Be Vigilant √ Profile like crazy √ Consider performance from day one √ Get your priorities straight Joseph Smarr, Plaxo, Inc.
Conclusion: Avoid making the same mistakes we did - Make the browser happy … and it will make you happy - Web browsers are more like mobile phones than desktops - - Limited, flimsy, temperamental platform being stretched beyond its initial design goals But everyone’s got one, so it’s still the best place to be Don’t push the limits unless you have to - Often, small quick-loading pages with AJAX interactions is best - Sometimes you really do need rich, interactive controls Joseph Smarr, Plaxo, Inc.
Just Remember: Everything You’ve Been Taught is Wrong - Think about performance — early and often - Write as little code as you need — each line has a cost - Do what the browser wants (whenever possible) - Remember the high-performance Java. Script mantra: - Be lazy - Be responsive - Be pragmatic - Be vigilant Joseph Smarr, Plaxo, Inc. http: //Joseph. Smarr. com
Скачать презентацию High-Performance Java Script Why Everything You ve Been Taught
879ff0a8ad1e88a5948fffa0791e5668.ppt