Responsive Svelte ... exploring Svelte's reactivity

This talk is focused on a better understanding of Svelte's reactivity. We will do this from an "observer perspective" - by visualizing it first-hand (right in your application)!

There's a bit of a mystery behind some of these concepts. We will delve into some lesser-known detail (that you may have not considered)! The hope is you will come away with more insight, and be better informed on how to use this awesome product!

The session will delve into:

- Visualizing Svelte's reactivity right in your application, through diagnostic probes. This provides a very clear insight on what Svelte is doing (seeing the dynamics all around you "on the fly")!

- Svelte's management of your JavaScript snippets
* both code-snippets (Reactive Statements/Declarations)
* and html-snippets (Interpolation)

- Svelte's Reactive Triggers
* both Dependency Monitoring
* and Staleness Detection (highlighting the difference between primitive and object types)

- Svelte's Re-Render Optimization
* showing the difference between interpolation (executing JS snippets)
* and re-rendering DOM fragments (a heavyweight operation)

This talk is an adaptation of my article on the same topic (found here: https://bit.ly/ResponsiveSvelte)

RESOURCE LINKS:

- Presentation Screencast: https://bit.ly/r-svelte-pres
- Presentation Resources: https://bit.ly/r-svelte
- Article: https://bit.ly/ResponsiveSvelte

Transcript

1. Kevin Bridges
   Applied Software Technologies
   kevin@wiiBridges.com
   @kevinast
   https://bit.ly/r-svelte
   slides, syllabus, REPL, and article!
   

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2. https://bit.ly/r-svelte
   slides, syllabus, REPL, and article!
   Deep Dive
   Observer Perspective
   Mystery
   Improved Insight
   

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3. Svelte Reactivity
   

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4. user: {
   name: 'Jenny',
   phone: '867-5309',
   }
   Svelte Store
   Svelte Interpolation
   GreetUser.svelte
   Svelte Reactivity
   

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5. GreetUser.svelte
   Svelte Reactivity
   

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6. Svelte Reactivity
   snippet:
   any JavaScript expression that Svelte reactively manages
   and invokes when it's dependent state changes
   SideBar (Terminology) …
   1. code-snippet
   found in tag, demarked with $: label<br/>2. html-snippet<br/>found in html markup, delineated with curly braces: {…}<br/>… svelte refers to this as: “Reactive Statements”<br/>… svelte refers to this as: “Interpolation”<br/>

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7. Svelte is soo KOOL!
   

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8. Svelte is soo KOOL!
   1975
   1969 1995 2006 2010 2019
   is Svelte soo KOOL?
   

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9. Primarily it's unique approach to reactivity
   it's "baked right in"
   rather like "magic“!
   The Svelte compiler:
   1) Isolates JS snippets
   … that provides our dynamics
   2) Identifies dependencies
   3) Monitors staleness
   4) Re-executes as needed
   … updating DOM fragments
   GreetUser.svelte
   Svelte is soo KOOL!
   Dependents
   Is Stale?
   Re-executes
   updating
   

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10. Exploring Reactivity
    

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11. I want to see Svelte’s Reactivity IN ACTION !
    In so doing:
    • become more grounded in Svelte philosophy
    • give insight on Svelte Heuristics
    … dependency monitoring
    … reactive triggers
    … DOM updates
    • better appreciate “all the reactivity around us”
    May just discover some detail we hadn’t considered!
    Exploring Reactivity
    

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12. Diagnostic Logging Probes
    Original:
    With Logging Probes:
    Phone section fired
    Ex: When phone changes, logs:
    Exploring Reactivity
    

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13. Diagnostic Logging Probes
    GreetUser.svelte
    Monitor
    Setup
    

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14. Diagnostic Logging Probes
    GreetUser.svelte
    

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15. Advanced Diagnostics
    logs are great, but …
    is there a way to Visualize Svelte's Reactivity "right in our app"?
    

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16. ReflectiveCounter
    Advanced Diagnostics
    

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17. ReflectiveCounter
    Usage:
    1. Monitor
    a) html-snippet:
    b) code-snippet:
    2. Report (common to both):
    Advanced Diagnostics
    

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18. Advanced Diagnostic Probes
    Monitor
    Report
    Setup
    GreetUser.svelte
    

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19. Advanced Diagnostic Probes
    GreetUser.svelte
    

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20. Re-Render Analysis
    Unexpected Results!
    

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21. Re-Render Analysis
    

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22. Svelte Dependency Monitoring
    

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23. Svelte Dependency Monitoring
    Object vs. Primitive
    Object:
    “Staleness Granularity” is the
    object (not individual content)
    Primitive:
    To be considered “Stale”, the value
    must change (Identity Semantics)
    

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24. Is Svelte producing redundant and unnecessary
    re-renders of our DOM fragments?
    Re-Render Analysis
    

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25. Svelte optimizes this!
    … discussed later
    Is Svelte producing redundant and unnecessary
    re-renders of our DOM fragments?
    Re-Render Analysis
    

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26. App-Based Reactivity Tweaks
    

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27. Basic Thrust:
    move reflexivity …
    • FROM: html-snippets
    • TO: code-snippets
    App-Based Reactivity Tweaks
    

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28. Fine Tune Svelte's Dependency Management
    by
    Normalizing referenced state into primitive types
    App-Based Reactivity Tweaks
    1. Finer Grained Dependency Management
    Before …
    GreetUser.svelte
    

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29. Fine Tune Svelte's Dependency Management
    by
    Normalizing referenced state into primitive types
    App-Based Reactivity Tweaks
    1. Finer Grained Dependency Management
    After …
    GreetUser.svelte
    

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30. App-Based Reactivity Tweaks
    1. Finer Grained Dependency Management
    GreetUser.svelte
    

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31. Normalize conditional logic into primitive types
    App-Based Reactivity Tweaks
    2. Preresolve Variations
    GreetUser.svelte
    Before …
    

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32. Normalize conditional logic into primitive types
    App-Based Reactivity Tweaks
    2. Preresolve Variations
    GreetUser.svelte
    After …
    

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33. App-Based Reactivity Tweaks
    2. Preresolve Variations
    GreetUser.svelte
    

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34. Svelte's Re-Render Optimization
    Is Svelte producing redundant and unnecessary
    re-renders of our DOM fragments?
    

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35. Is Svelte producing redundant and unnecessary
    re-renders of our DOM fragments?
    Could Svelte be optimizing this?
    it would make sense for two reasons:
    1. Svelte's overly broad dependency granularity
    2. App classification grouping - generating same result from
    multiple dependent values
    Svelte's Re-Render Optimization
    

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36. Is Svelte producing redundant and unnecessary
    re-renders of our DOM fragments?
    Svelte's Re-Render Optimization
    Could Svelte be optimizing this?
    it would make sense for two reasons:
    1. Svelte's overly broad dependency granularity
    2. App classification grouping - generating same result from
    multiple dependent values
    

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37. Svelte's reflexivity is very efficient!
    1. The component's DOM representation is highly optimized
    2. Dynamic content is gleaned from executing html-snippets
    3. Reflection is triggered by dependent state changes
    4. DOM updates occur only when the content has actually changed!
    Svelte's Re-Render Optimization
    

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38. Svelte's reflexivity is very efficient!
    knowing what we know now
    Are App-Based Reactivity Tweaks Necessary?
    Seriously …
    was this really
    Necessary?
    Svelte's Re-Render Optimization
    

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39. Svelte's reflexivity is very efficient!
    knowing what we know now
    Are App-Based Reactivity Tweaks Necessary?
    most likely
    only in rare cases
    consider this:
    1. Large reflection/re-render count variance
    2. High overhead in html-snippet execution
    3. Same html-snippet needed in multiple places
    Better understand the finer
    characteristics of Svelte's reactivity!
    Seriously …
    was this really
    Necessary?
    Svelte's Re-Render Optimization
    

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41. Enhance ReflectiveCounter to provide
    BOTH:
    • reflexive counts
    -and-
    • re-render counts
    HINT … the invocation will change
    • FROM:
    • TO:
    

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43. 1.We can visualize Svelte's Reactivity (right in our app)
    • Diagnostic Logs: logically-ORed expressions
    • ReflectiveCounter: new utility belt
    2.Dependent State and Reactivity
    • Primitives: trigger reactivity only when the value changes (based on identity semantics)
    • Objects: trigger reactivity per the entire object, not individual content
    3.Svelte's reflexivity is very efficient!
    • The component's DOM representation is highly optimized
    • Dynamic content is gleaned from executing html-snippets
    • Reflection is triggered by dependent state changes
    • DOM updates occur only when the content has actually changed!
    4.App can "fine tune" reactivity (as needed)
    

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44. Kevin Bridges
    Applied Software Technologies
    kevin@wiiBridges.com
    @kevinast
    https://bit.ly/r-svelte
    slides, syllabus, REPL, and article!
    

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