Smarr Oscon 2007
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Smarr Oscon 2007 Smarr Oscon 2007 Presentation Transcript

  • High-Performance JavaScript: 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)
      • JavaScript Wormhole (OSCON 06)
    http://JosephSmarr.com
  • 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, 15M+ users
      • Backed by Sequoia, Ram Shriram, Tim Koogle, et al
    http://www.plaxo.com
  • Plaxo Online AJAX Desktop beta.plaxo.com
    • Flexible desktop
    • Contacts
    • Calendar
    • Tasks
    • Notes
    • Sync dashboard
    • Pulse
    • Profile / settings
  • Plaxo Online AJAX Desktop beta.plaxo.com
    • Flexible desktop
    • Contacts
    • Calendar
    • Tasks
    • Notes
    • Sync dashboard
    • Pulse
    • Profile / settings
  • Plaxo Online AJAX Desktop beta.plaxo.com
    • Flexible desktop
    • Contacts
    • Calendar
    • Tasks
    • Notes
    • Sync dashboard
    • Pulse
    • Profile / settings
  • 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!)”
  • 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…
  • 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
      • JavaScript code is parsed & interpreted every time  cost per line of source code
  • Why High-Performance JavaScript Matters
    • Everyone is amazed by fast apps
      • It hardly matters what else they do!
    • Everyone hates slow apps
      • 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:
  • The High-Performance JS Mantra
    • Be Lazy
    • Be Responsive
    • Be Pragmatic
    • Be Vigilant
  • The High-Performance JS Mantra
    • Be Lazy: Nothing is faster than doing nothing
    • Be Responsive
    • Be Pragmatic
    • Be Vigilant
  • Write less code
    • Initial parsing of JavaScript is often a major bottleneck
      • No JIT, no cached object code, interpreted every time
      • Parse time is non-linear in the size of total JavaScript?
    • 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 <500K JS uncompressed
    Be Lazy: Nothing is faster than doing nothing
  • Total code size of some AJAX apps
  • Write less code
    • Minimize the JavaScript 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
    Be Lazy: Nothing is faster than doing nothing
  • Load JavaScript on-demand
    • Once you’ve written less code, load it only as-needed
      • 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
    Be Lazy: Nothing is faster than doing nothing “ I work hard at being lazy” Ryan “Roger” Moore
  • 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
      • But have to know when to invalidate the cache
    • Don’t keep hidden UI up-to-date behind the scenes
      • 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
    Be Lazy: Nothing is faster than doing nothing
      • Never pre-draw hidden UI
      • Never pre-draw hidden UI
      • Never pre-draw hidden UI
      • Never pre-draw hidden UI
      • Never pre-draw hidden UI
  • How to Be Lazy
    • Write less code!
    • Load JS on-demand
    • Draw UI as late as possible
    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
  • 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)
    Be Responsive: Jump when the user says jump
      • Load your app in stages
      • Load your app in stages
      • Load your app in stages
      • Load your app in stages
      • Load your app in stages
      • Load your app in stages
      • Load your app in stages
  • 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 setTimeout(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 (~100msec faster!)
      • Demo: http://josephsmarr.com/oscon-js/yield.html
    Be Responsive: Jump when the user says jump
  • Cache backend responses
    • 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
      • Do the easy cases, but beware of too much update code
      • Worst case = trash cache and re-fetch = first-time case
    Be Responsive: Jump when the user says jump “ Data structures and AJAX—together at last!” Glenn “Fiddich” Dixon
  • How to Be Responsive
    • Minimize initial perceived loading time
    • Yield early and often for responsive UI
    • Cache API responses with data-manager layer
    Be Responsive: Jump when the user says jump
  • The High-Performance JS Mantra
    • Be Lazy
    • Be Responsive
    • Be Pragmatic: Don’t make things even harder
    • Be Vigilant
  • Play to the browser’s strengths
    • Avoid DOM manipulation; use innerHTML 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
    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)
    Be Pragmatic: Don’t make things even harder
  • Inline initial API calls & HTML
    • Tempting to load blank page and do everything in JavaScript
      • Have to redraw UI dynamically; don’t want two copies of UI code
    • Problem: initial load is usually too slow
      • 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
    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
    Be Pragmatic: Don’t make things even harder
  • The High-Performance JS Mantra
    • Be Lazy
    • Be Responsive
    • Be Pragmatic
    • Be Vigilant: Only you can prevent slow web apps
  • Profile like crazy
    • Bottlenecks abound and are usually not obvious
      • Use firebug’s profiler (Joe Hewitt, you rule!  )
      • Use timestamp diffs and alerts
      • 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)
    Be Vigilant: Only you can prevent slow web apps
  • Firebug is your friend
  • 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
    Be Vigilant: Only you can prevent slow web apps
    • 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!)
    Get your priorities straight Be Vigilant: Only you can prevent slow web apps “ Performance first, features second!” Todd & Cam
  • How to Be Vigilant
    • Profile like crazy
    • Consider performance from day one
    • Get your priorities straight
    Be Vigilant: Only you can prevent slow web apps
  • 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
  • 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 JavaScript mantra:
      • Be lazy
      • Be responsive
      • Be pragmatic
      • Be vigilant
    http://JosephSmarr.com