ByteArrays, Vectors, Tuples

• ByteArray class, converts from Array
  • Array.map etc. work on it, albeit generically
• Parameterized type Vector.<T>
  • Dense, optionally fixed length
  • Vector.<T>(length : uint = 0, fixed : boolean = false)
• ByteArray could be subsumed by Vector.<byte>
  • If we are willing to add a byte type
• Structural array type A = [int, string, boolean] is a tuple
  • Not a named Tuple type!
  • Fixed length with type constraints
  • Type-checked compatibility with Array

Type System Trade-offs

• We believe untyped objects will abound forever
• But typed APIs, including structural types, will emerge
• Nominal (class) hierarchies (DOM, Flex, etc.) likely too
  • But they won't take over the Web
  • So we're not turning JS into Java
• Most common case: Untyped code calling Typed API
• Another important case: class matching structural type

Structural Types as Contracts

• Given function f(a : {p: int, q: string}) ...
  • Assume it's a structurally typed API method
• What does f({p: 42, q: "hi"}) check, and when?
• Use cases want early and deep checking
  • An untyped object could mutate after the check
  • Checking every read too costly, yet still incomplete
  • See MochiKit's isArrayLike, isDateLike
• Given a class C with the right instance vars,
  • passing f(new C(42, "hi")) can go fast

Performance Trends

• "Fastest browser on the planet" i-bench bragging
• Pure JS performance not critical (yet, for common cases)
• DOM and rendering dominate critical paths, but:
  • DOM bindings hide JS dynamic typing costs
  • Developers are pushing hard at the frontiers
• John Resig wrote and collected some benchmarks
• http://ejohn.org/apps/js-speed/results/

New Projects

ActionMonkey

• Mascot wannabe:
• Merge Tamarin and SpiderMonkey
• Targeting Mozilla 2 release, beta next year
• First stage integrates Tamarin's Garbage Collector
• Later stages include trace-based JITing

IronMonkey

• Inspiration:
• Map IronPython and IronRuby to Tamarin
  • Avoid forking C# source using Mono C# compiler
  • Bytecode translation a la IKVM, JaCIL
• Led by Seo Sanxiyn of FePy and PyPy fame

ScreamingMonkey

• Goal: support Tamarin in other browsers
• Led by Mark Hammond of Windows Python fame
• First target: IE integration as an ActiveScript engine
• Handle these RFC 4329 content <script> type= values:
  • application/ecmascript;version=4
  • application/javascript;version=2
• Other browser integrations to follow

The Truth About JavaScript

• JavaScript is...
• Occasionally a curse
• Often a blessing, formerly in disguise
• Spreading from the browser (Rhino on Rails)
• Growing muscle and speed
• Upgradeable in browsers (even in IE)
• The 'J' in AJAX The 'j' in Ajax?

Vlad's Photos Demo

• Photos

Finis