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Back to the future of JS II: Beyond what we can foresee

Back to the future of JS II: Beyond what we can foresee

Willian Martins

February 07, 2019

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  1. @wmsbill Toy example List of shapes 
 {size, color, type}

    Log all circles, red squares and big blue triangles
  2. @wmsbill The majority of the languages uses pattern matching as

    an expression I wish it could be landed in JS as an expression as well Can be achieved using do expression proposal. Pattern matching as a statement
  3. @wmsbill Function composition in JS Combining two or more functions

    to create a new function Composing function is a common task in JS nowadays We can achieve it in a bunch of ways
  4. @wmsbill Pipeline operator |> It is a syntax sugar for

    function composition It creates a way to streamline a chain of functions
  5. @wmsbill Smart Pipeline proposal Two types bare style and topic

    style () or [] are disallowed in bare style When () or [] is needed, topic style is used # token is subject to change
  6. @wmsbill F# Pipeline Proposal Extends the minimal proposal with an

    await step Await step waits for the resolution of the previous step
  7. @wmsbill Nice addition for creating function composition in a streamlining

    way Minimal proposal has 2 caveats Smart pipeline adds a token F# adds an await step Pipeline operator - summary
  8. @wmsbill F# pipeline is simple and easier to reason about

    The Introduction of # token could be introduced once F# proposal was merged Babel 7.3 has shipped smart pipeline proposal. Pipeline operator - rollout strategy
  9. @wmsbill JS cold start Ship less JS 150kb of Compressed

    JS is different of 150 kb of image Lazy load your JS
  10. @wmsbill Start-up phase: Download, Parse, Compilation Runtime phase: Run, Optimization/

    Deoptimization, Bailing out. Tear down phase: Garbage collection JS “lifecycle” steps
  11. @wmsbill It is crucial for the application perceived performance. Parsing

    + compilation can take up to 30%* of main thread time 1MB os uncompressed JS can take 1s or more in average Mobile device. The cold start-up problem *Numbers may vary from depending on the js engine
  12. @wmsbill New over-the-wire format for JS Based on a binary

    encoding of a simplified custom AST. Potentially decrease the cold start-up of large JS applications Browsers that doesn’t support it, still loads a .js file Binary AST
  13. @wmsbill Early Prototype created on SpyderMonkey Using a grammar based

    on SM internal AST format Facebook static newsfeed as a benchmark The PoC
  14. @wmsbill AST size slightly smaller than JS Create a full

    AST from plain JS took between 500 and 800 ms Time for creating full AST was twice as fast as before The PoC - the results
  15. @wmsbill Plain binary AST is a good perf win Extra

    annotations enables dead code elimination Further enhancements can enable streaming compilation of the binary AST. Looking beyond