How late is later? A lazy loading solution on the edge between very clever and incredibly mad.

Reducing the loading time of a web application is a well known problem. Developers need to make sure the browser only downloads the code that is strictly necessary to bootstrap the application and leave the rest for later. This is what we commonly call lazy loading.

But when is later? When is the right time to lazy load?

When users interact with our applications there is a good chance they won't use all the provided features. Why lazy load code that is not needed then? Front-end code can be logically split into 3 sets:

Code required to bootstrap.
Code needed for the core functionality. It should be lazy loaded as soon as the bootstrap code has been delivered and parsed.
Code that may not even be necessary, or that is required only when a particular feature is used, and is therefore strictly dependent on the actions users perform within the context of the application. This means that this code can/should be loaded on demand.
This talk shows how JavaScript code - functions and objects - can be delivered to the browser on demand, thus reducing the perceived loading time of a web application.

Video here: http://www.ustream.tv/recorded/25243564

Transcript

1. How late is later?
   

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2. A lazy loading solution on
   the edge between very
   clever and incredibly mad."
   "
   Massimiliano Marcon"
   @mmarcon"
   "
   frontendconf.ch • September 7th 2012
   

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3. What I do at Nokia Maps
   

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4. I
   "
   LAZY "
   LOADING
   

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5. WTF
   !!1!!! !!
   !!2!!! !!
   !!3!!!!
   !!4!!! !!
   !!5!!!!!
   !!6!!!!!
   !!7!!!!
   !!8!!! !!
   !!9!!! !!
   !10!!!
   !!
   !11!!! !!
   !12!!!!!
   !13!! !!
   
   

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6. Not good either
   !1!!
   !!
   
   

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7. The problem
   The amount of code the
   browser loads affects
   performance and influences the
   perceived loading time.
   

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8. LESS CODE TO LOAD
   

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9. Is all that code really necessary?
   NO!
   

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10. THE STORY OF A HAPPY USER
    

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11. I, as a user…
    Open my browser and start typing a URL
    in my address bar.
    

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12. Bootstrap ASAP
    1!
    

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13. Dude, that
    was fast!
    

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14. 2!
    Enrich the Experience
    

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15. 3!
    Load remaining code on demand
    

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16. 
    Load shims on demand
    

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17. 1!Bootstrap !
    2!Enrich!
    3!On Demand!
    

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18. WHERE EVERYTHING BEGAN
    

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20. …possibly load UI components on
    demand
    •  What does on demand mean?
    

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21. “In distributed computing, code on
    demand is a general term for any
    technology that sends executable
    software code from a server computer to
    a client computer upon request from the
    client's software”
    ― Wikipedia
    

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22. HOW CAN WE DO IT?
    

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23. Require.js
    Modules
    ON DEMAND
    Dependencies
    

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24. callback-require
    !1!!require(['require',!
    !!
    !2!!!!!!!!!!!'modules/3rd:party/jquery'],!function(require,!$)!{!
    !!
    !3!!!!!!$('button').on('click',!function(e){! !!
    !4!!!!!!!!!!require(['modules/dialog'],!function(dialog){! !!
    !5!!!!!!!!!!!!!!dialog.create($('Hello!world'),!'My!Dialog');!
    !!
    !6!!!!!!!!!!});!
    !!
    !7!!!!!!});!
    !!
    !8!!});!!
    
    

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25. callback-require for shims
    !!1! !require(['require',! !!
    !!2! !!!!!!!!!!'modules/3rd:party/jquery'],!function(require,!$)!{! !!
    !!3! !! !!
    !!4! !!!!!var!SUPER_DUPER_APP!=!function(JSON){! !!
    !!5! !!!!!!!!!//Do!some!fancy!stuff!here!with!my!application.! !!
    !!6! !!!!!!!!!//At!this!poit!all!JSON.parse/JSON.stringify!will!be!available!for! !!
    !!7! !!!!!!!!!//ALL!browsers.!Isn't!that!cool?!! !!
    !!8! !!!!!};! !!
    !!9! !! !!
    !10! !!!!!if(typeof!JSON.parse!===!'function')!{!!!
    !11! !!!!!!!!!//Oh,!we've!got!native!JSON!support! !!
    !12! !!!!!!!!!SUPER_DUPER_APP(JSON!/*Native!one*/);! !!
    !13! !!!!!}! !!
    !14! !!!!!else!{! !!
    !15! !!!!!!!!!//Uhmm...!I!smell!IE!!16! !!!!!!!!!require(['shims/json'],!function(){! !!
    !17! !!!!!!!!!!!!!//No!need!to!use!parameters,!this!shim!just!creates! !!
    !18! !!!!!!!!!!!!!//a!global!JSON!object.! !!
    !19! !!!!!!!!!!!!!SUPER_DUPER_APP(JSON!/*Shimmed!one*/);! !!
    !20! !!!!!!!!!});! !!
    !21! !!!!!}! !!
    !22! !}); !!
    

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26. CLEVERNESS or MADNESS?
    

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27. Custom solution
    !1!!$(function(){! !!
    !2!!!!!!$('button').on('click',!function(e){! !!
    !3!!!!!!!!!!$.onDemand.use('dialog').done(function(dialog){! !!
    !4!!!!!!!!!!!!!!dialog.create($('Hello!world'),!'My!Dialog');!
    !!
    !5!!!!!!!!!!});!
    !!
    !6!!!!!!});!
    !!
    !7!!});!!
    
    

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28. How does this work?
    !!1! !OnDemand.prototyte.firstLoad!=!function(fn,7args,7context){! !!
    !!2! !!!!!var!script,!deferred!=!$.Deferred(),!rv;!!!
    !!3! !! !!
    !!4! !!!!!if!(isFn(that._proxy[fn]))!{! !!
    !!5! !!!!!!!!!rv!=!that._proxy[fn].apply(context,!args);! !!
    !!6! !!!!!!!!!deferred.resolve(rv);! !!
    !!7! !!!!!}!
    !!
    !!8! !!!!!else!if(isObj(that._proxy[fn]))!{! !!
    !!9! !!!!!!!!!deferred.resolve(that._proxy[fn]);! !!
    !10! !!!!!}!
    !!
    !11! !!!!!else!{! !!
    !12! !!!!!!!!!script!=!this.fn2script(fn);! !!
    !13! !!!!!!!!!if!(!script)!{! !!
    !14! !!!!!!!!!!!!!return;! !!
    !15! !!!!!!!!!}! !!
    !16! !!!!!!!!!$.getScript(script).done(function(){!!!
    !17! !!!!!!!!!!!!!var!rv;! !!
    !18! !!!!!!!!!!!!!if!(isFn(that._proxy[fn]))!{! !!
    !19! !!!!!!!!!!!!!!!!!rv!=!that._proxy[fn].apply(context,!args);! !!
    !20! !!!!!!!!!!!!!}! !!
    !21! !!!!!!!!!!!!!else!if!(isObj(that._proxy[fn]))!{! !!
    !22! !!!!!!!!!!!!!!!!!rv!=!that._proxy[fn];! !!
    !23! !!!!!!!!!!!!!}! !!
    !24! !!!!!!!!!!!!!deferred.resolve(rv);! !!
    !25! !!!!!!!!!}).fail(function(){! !!
    !26! !!!!!!!!!!!!!deferred.reject('OnDemand!failed!to!load!script!'!!+!script);! !!
    !27! !!!!!!!!!});!!!
    !28! !!!!!}!
    !!
    !29! !!!!!return!deferred.promise();! !!
    !30! !};!
    !!4! !!!!!if!(isFn(that._proxy[fn]))!{! !!
    !!5! !!!!!!!!!rv!=!that._proxy[fn].apply(context,!args);!
    !!6! !!!!!!!!!deferred.resolve(rv);! !!
    !!7! !!!!!}! !!
    !!8! !!!!!else!if(isObj(that._proxy[fn]))!{! !!
    !!9! !!!!!!!!!deferred.resolve(that._proxy[fn]);!!!
    !10! !!!!!}!!
    !16! !!!!!!!!!$.getScript(script).done(function(){! !!
    !17! !!!!!!!!!!!!!var!rv;! !!
    !18! !!!!!!!!!!!!!if!(isFn(that._proxy[fn]))!{! !!
    !19! !!!!!!!!!!!!!!!rv!=!that._proxy[fn].apply(context,!args);!!!
    !20! !!!!!!!!!!!!!}!
    !!
    !21! !!!!!!!!!!!!!else!if!(isObj(that._proxy[fn]))!{!
    !!
    !22! !!!!!!!!!!!!!!!!!rv!=!that._proxy[fn];! !!
    !23! !!!!!!!!!!!!!}!
    !!
    !24! !!!!!!!!!!!!!deferred.resolve(rv);! !!
    !25! !!!!!!!!!})!
    

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29. PERFORMANCE
    

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30. “0.1 second is about the limit for having
    the user feel that the system is reacting
    instantaneously…”
    ― Nielsen, Usability Engineering
    

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31. Let’s relax the definition of"
    on demand
    •  On demand is not strictly on click.
    •  On demand is right before we expect
    the code to be needed.
    

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32. BEYOND MADNESS
    

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33. window.performance
    !1!
    !//!returns!a!duration!in!milliseconds! !!
    !2!
    !function!getUserPerceivedLoadingTime()!{! !!
    !3!
    !!!return!!!
    !4!
    !!!!!window.performance.timing.loadEventStart!!!
    !5!
    !!!!!!:!window.performance.timing.navigationStart;! !!
    !6!
    !}; !!
    
    http://j.mp/w3c-window-performance
    

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34. Q&A
    

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35. DO IT. DO IT WISELY.
    

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36. If you are interested in these
    slides and some other material
    related to this presentation just
    follow @mmarcon."
    
    Feedback: http://j.mp/rate-mmarcon
    

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37. Thank you.
    

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