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Paul Bakaus, Liferay

Ignore the DOM
Why is JavaScript
                             slow?


Paul Bakaus, Liferay                       2
JS Performance Stack

                           CSS




  JavaScript                         Displayed in Browser
                          DOM



                         Rendering

Paul Bakaus, Liferay                                    3
JS Performance Stack

                          CSS


                                   Rendered
  JavaScript                       representation
                          DOM



                         Parsing

Paul Bakaus, Liferay                                4
JS Performance Stack

‣ JavaScript itself is not what
     makes JavaScript slow
‣ If we could forget out the
     parsing/rendering,                   Awwww!
     JavaScript would be                 How I hate
                                         the DOM!
     lightning fast




Paul Bakaus, Liferay                                  5
But if we were to do
                         that..


Paul Bakaus, Liferay                    6
..we‘d have a beautiful
        command line application!




Paul Bakaus, Liferay                7
So what can we do?



Paul Bakaus, Liferay                    8
Can we remove CSS?

‣ CSS makes our pages
     beautiful
‣ DOM Layer 2 for stylesheets
     is actually very fast


                       No way!

Paul Bakaus, Liferay                        9
How about DOM?

         ‣ The DOM gives us representations of objects
             in JS
         ‣ It is used for various tasks, most often to
             select and change an element




Paul Bakaus, Liferay                                     10
Two systems
 Isolated environment          Open environment

                                External
                                 source




                                           External
                                            source




Paul Bakaus, Liferay                                  11
Two systems
 Isolated environment          Open environment

                                External
                                 source




                                           External
                                            source




Paul Bakaus, Liferay                                  12
Old School!

      Build custom solutions!
                                             Wait!
                                I don‘t have the time for that!


        ..then use a library!

                                   ..but that still consumes
                                       too much time :(


             does it really?

Paul Bakaus, Liferay                                              13
A sample application
                     using jQuery



Paul Bakaus, Liferay                    14
Patterns



Paul Bakaus, Liferay              15
Canvas

‣ Imagine you‘re in a
     <canvas> element
‣ No DOM
‣ No event system

                 then plan what you
                   explicitely need

Paul Bakaus, Liferay                  16
Mutation events

                 W3C                   IE

   ‣ DOMNodeInserted           ‣ onpropertychange
   ‣ DOMNodeRemoved
   ‣ DOMAttrModified




Paul Bakaus, Liferay                                17
..more

‣ Build your own event
     model (through
     delegation)
‣ Control the output -
     know, how many
     elements are on your
     page




Paul Bakaus, Liferay            18
..even more

‣ Cache as much as possible
‣ In frameworks, reuse selectors and offsets
‣ Work with template nodes




Paul Bakaus, Liferay                           19
Thanks for your
                         attention!



Paul Bakaus, Liferay                     20
Contact



 ‣ paul.bakaus@gmail.com
 ‣ paulbakaus.com




Paul Bakaus, Liferay             21

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Ignore the DOM

  • 2. Why is JavaScript slow? Paul Bakaus, Liferay 2
  • 3. JS Performance Stack CSS JavaScript Displayed in Browser DOM Rendering Paul Bakaus, Liferay 3
  • 4. JS Performance Stack CSS Rendered JavaScript representation DOM Parsing Paul Bakaus, Liferay 4
  • 5. JS Performance Stack ‣ JavaScript itself is not what makes JavaScript slow ‣ If we could forget out the parsing/rendering, Awwww! JavaScript would be How I hate the DOM! lightning fast Paul Bakaus, Liferay 5
  • 6. But if we were to do that.. Paul Bakaus, Liferay 6
  • 7. ..we‘d have a beautiful command line application! Paul Bakaus, Liferay 7
  • 8. So what can we do? Paul Bakaus, Liferay 8
  • 9. Can we remove CSS? ‣ CSS makes our pages beautiful ‣ DOM Layer 2 for stylesheets is actually very fast No way! Paul Bakaus, Liferay 9
  • 10. How about DOM? ‣ The DOM gives us representations of objects in JS ‣ It is used for various tasks, most often to select and change an element Paul Bakaus, Liferay 10
  • 11. Two systems Isolated environment Open environment External source External source Paul Bakaus, Liferay 11
  • 12. Two systems Isolated environment Open environment External source External source Paul Bakaus, Liferay 12
  • 13. Old School! Build custom solutions! Wait! I don‘t have the time for that! ..then use a library! ..but that still consumes too much time :( does it really? Paul Bakaus, Liferay 13
  • 14. A sample application using jQuery Paul Bakaus, Liferay 14
  • 16. Canvas ‣ Imagine you‘re in a <canvas> element ‣ No DOM ‣ No event system then plan what you explicitely need Paul Bakaus, Liferay 16
  • 17. Mutation events W3C IE ‣ DOMNodeInserted ‣ onpropertychange ‣ DOMNodeRemoved ‣ DOMAttrModified Paul Bakaus, Liferay 17
  • 18. ..more ‣ Build your own event model (through delegation) ‣ Control the output - know, how many elements are on your page Paul Bakaus, Liferay 18
  • 19. ..even more ‣ Cache as much as possible ‣ In frameworks, reuse selectors and offsets ‣ Work with template nodes Paul Bakaus, Liferay 19
  • 20. Thanks for your attention! Paul Bakaus, Liferay 20
  • 21. Contact ‣ paul.bakaus@gmail.com ‣ paulbakaus.com Paul Bakaus, Liferay 21