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JavaScript World
The

Domination Plan at 16 Years
brendan@mozilla.org

• History

• Controversies

• Performance

• ES.next

• Demos

Thursday, October 27, 2011

History

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A very brief history

• Ten days in May 1995: “Mocha”, form validation, img rollovers, scripting of Java

• September 1995: “LiveScript” (did Netscape marketing go to Microsoft after?)

• December 1995: “JavaScript”, thanks to Bill Joy (a Sun Founder)

• 1996-1997: ECMA-262 Ed. 1, aka ES1, thanks to ECMA (now Ecma) TC39

• 1999: ES3: function expressions, RegExp, try/catch/ﬁnally, switch, do-while

• 2005: the Ajax revolution, followed by “The Ajax Experience”

• 2008: ES4 RIP, Harmony founded in July at the Oslo TC39 meeting
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• 2009: ES5: “use strict”, JSON, Object.create, etc.

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Netscape in 1995

• Netscape had 50-80% browser share during explosive early Web growth

• Microsoft low-ball buy-out attempt in late 1994 rebuffed

• Threat to Windows made explicit by Java and too much hype

• “Worse is Better!” - @pmarca channeling @rpg

• “We are doomed!” - engineering refrain

• Very narrow window in which to innovate and “get on ﬁrst”

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Pitch to me: come do “Scheme in the browser”

• One-shot opportunity to create the “HTML scripting language”

• By the time I joined, the Netscape/Sun “Java deal” cast long shadow

• Engineering VP: “make it look like Java” (I made it look like C and AWK)

• Argument by code demonstration became necessary

• I hacked the “Mocha” prototype in 10 days in May 1995

• And it showed. Mistakes (some recapitulating LISP) were frozen early

• I spent the rest of 1995 embedding in the browser, creating the DOM mozilla

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Primordial DOM
• Netscape lacked a
persistent DOM tree
model; it had only a
ﬂattened display list

• To avoid slowing page
load performance, I built
the primordial DOM
lazily from the display list

• Hence, document.write


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(credit for last two slides)

• Kleber & Jain, "Don't Let Third Parties Slow You Down" (Velocity 2010)

• Upshot: incremental/progressive/asynchronous code loading required for speed
with responsiveness (Java class loading counterexample)

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Initial design goals

• Make it easy for non-experts to copy/paste snippets of code into HTML

• Tolerate “minor” errors (e.g., missing semicolons)

• Simpliﬁed onclick, onmousedown, etc., event handling, inspired by HyperCard

• Pick a few hard-working, powerful primitives

• First class functions for procedural abstraction (AWK more than Scheme)

• Objects everywhere, prototype-based (Self, but only one parent per object)

• Leave all else out! mozilla

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Marketing, sigh

• Netscape management fretted: “Why two programming languages?”

• Answer: division of labor, specialization

• Java for high-priced components/widgets (applet/plugin model)

• “Mocha” for mass market web designers (glue between components)

• Primitive types vs. objects patterned after Java with LiveConnect in mind

• “Object-based”, not object-oriented (no class) -- cannot have JS/Robin-the-
boy-hostage encroaching on Java/Batman...
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Name games, the J word

• Then Netscape changed the name to “LiveScript”

• Finally, with Bill’s help on behalf of Sun, to “JavaScript” in December 1995

• Mostly a marketing scam

• Engineering pressure to “be like Java” did cause us to follow Java into some
dead ends (Date inherited y2k bugs from java.util.Date)

• In the last decade Java has almost disappeared on the client side of the Web

• Java is top moneymaker as malware kit vector (per Brian Krebs)
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• Now behind a click-to-activate barrier/whitelist in Chrome

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JS in two slides

• Objects map strings to values (properties):

var obj = new Object;
obj[“prop”] = 42;!! ! // => obj.prop
obj[“0”] = “hello”;! ! // => obj[0]

other = {prop: 99, 0: “goodbye”}; // an object literal
array = [0, 1, 2, 3, 4, 5, 6, 7]; // array.length == 8

• Functions are ﬁrst-class objects:

function fact(n) {
return (n <= 2) ? n : n * fact(n-1);
}
fact.desc = “Factorial function”; mozilla
result = array.map(fact);

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JS in two slides (2)

• Methods are function-valued properties:

obj.frob = function (n) {
this.prop += n;
};

obj.frob(6);! ! // => obj.prop == 48

• Top-level scope is an object. Implicit conversion. Oops.

grob = obj.frob;! // => assign a global method, grob
grob(6);! ! !
! // => undefined + 6 == NaN
prop = “hello”;! // => reset global prop to string
grob(6);! ! !
! // => prop == “hello6”
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Closures

• function Y(g) {
return function (f) {return f(f);}(
function (f) {return g(function (x) {
return f(f)(x);
});
});
}

• var fact = Y(function (fact) {
return function (n) {
return (n <= 2) ? n : n * fact(n-1);
}
});

alert(fact(5));! => 120
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Prototypes

• All user-deﬁned functions can construct:

function Car(make, model) {
this.make = make;
this.model = model;
}
myCar = new Car(“Honda”, “Fit”);

• All user-deﬁned functions have a prototype property:

Car.prototype.color = “black”;!// default color
old = new Car(“Ford”, “T”);!
! // black Model T
myCar.color = “silver”;! ! ! // silver Honda Fit

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• Powerful when combined with closures

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Controversies

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Why no bytecode?

• Top engine implementors won't agree on one bytecode

• Lowering JS semantics too far from source is future-hostile

• Versioning is anathema on the web (JVM, Flash counterexamples)

• JS with a few evolutionary steps is already a decent “bytecode”

• TypedArrays, binary data: machine storage types

• Type inference, runtime type/value proﬁling, proposed runtime guards

• Compressed AST encoding a la JSZap [Livshits, Zorn] is likelier mozilla

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Why no multi-VM browser integration

• Advantage: use canonical implementations, e.g., CPython for Python

• Drawbacks: those canonical implementations are not ready for the web

• Versioning independent of browser releases => dynamic linking/update

• OS-specific low-level APIs, toolchain-specific FFIs

• Insufficient fuzz-testing and web security engineering

• Proxies among disjoint heaps require non-distributed garbage-cycle collection

• Proxies among different languages a tall order otherwise mozilla

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No browser wins by taking overlarge risks

• Previous slide from Collin Jackson’s USENIX Security 2011 invited talk, titled
“Crossing the Chasm: Pitching Security Research to Mainstream Browser
Vendors” [slides]

• Features are not free

• Mozilla commissioned optional CPython integration work by Mark Hammond

• Used by only one embedder

• No CPython distribution for Windows or Mac OS X

• High sunk and recurring engineering costs mozilla

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Why no single multi-language VM?

• IPR, NIH bad reasons, but...

• Such VMs always build in advantages for one “lead language” (e.g., Java)

• Rest of pack are incomplete copies of canonical implementations (Jython)

• Large companies can perhaps afford to strive for completeness over time,
other browser vendors cannot

• See previous slide

• JS as compiler target dramatically on the rise -- are we already here?

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JS has awful warts!

• So use JSLint, JSHint, ADsafe, or better

• Two example from primordial JS:

• function f(o,x) { with (o) return x; } -- o.x or parameter x?

• function g(s) { eval(s); return function(){ return x; } }
cannot be analyzed to decide that s != “var x = ‘ha ha’”

• Fixed in ES5 strict mode, which removes with and gives eval its own scope

• ES.next (likely ES6) removes global object from scope chain: pure lexical scope
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• == and != are not equivalance relations (so use === and !==)

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Performance

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Performance progress - V8

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Tuning for SunSpider [Richards, Vitek, et al.]

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Recent progress - SpiderMonkey Type Inference

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ES.next

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The Harmony goals

• Be a better language for writing:

• complex applications

• libraries (including the DOM) shared by those applications

• code generators targeting the new edition

• Better tests, if not a testable (executable) speciﬁcation

• Adopt de facto standards where possible

• Keep versioning as simple and linear as possible

• Support a statically veriﬁable, object-capability subset mozilla

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Approved for ES.next

• let, const, function in block scope

f(“outer”);
function f(x) {
{ let x = “inner”; print(x); } // prints “inner”
print(x); // prints “outer”
}

• destructuring: let {x, y} = pt; let [s, v, o] = triple()

• parameter default values: function f(x, y=1, {z=2, w=3}) {...}

• rest, spread: function g(i, j, ...r) { return r.slice(i, j); }
let a = [0, 1, 2, 3], b = [...a, 4, 5, 6, 7],
o = new anyConstructor(...a),
z = variadic(...a, -1, ...b); mozilla

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More approved for ES.next

• proxies, weak maps: Proxy.create(handler, proto), new WeakMap

• modules:

module NewMath { export function sin(x) {...} }

module Prefetch = “http://your/url/here”;

• iterators, generators:

function* gen() { yield 1; yield 2; }

for (let i of gen()) print(i); // prints 1 and 2

• array comprehensions: return [x+y for x of a for y of b]

• generator expressions: let g = (x+y for x of a for y of b) mozilla

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Yet more approved for ES.next

• Binary data:

• const Point2D = new StructType({ x: uint32, y: uint32 }),
Color = new StructType({ r: uint8, g: uint8,
b: uint8 }),
Pixel = new StructType({ point: Point2D,
color: Color });

• const Triangle = new ArrayType(Pixel, 3);

• new Triangle([{ point: { x: 0, y: 0 },
color: { r: 255, g: 255, b: 255 } },
{ point: { x: 5, y: 5 },
color: { r: 128, g: 0, b: 0 } },
{ point: { x: 10, y: 0 },
color: { r: 0, g: 0, b: 128 } }]); mozilla

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String interpolation and templating

• Injection-safer string interpolation and domain-speciﬁc languages

• Backtick-quoted string desugars to a function call that operates on the literal
portions and substitution results:

• quasi`literalPart1${substitution}literalPart2` desugars to

• quasi({raw: ["literalPart1", "literalPart1"],
cooked: ["literalPart1", "literalPart1"]},
substitution)

• Multiline string literals w/o preﬁx: `literalPart1${substitution}
(yes, that was a newline!) literalPart2`
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• Multiline regexp literals: re`literalPart1${substitution}
(yes, that was a newline!) w+ literalPart2`
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Classes squeaked by, but face existential doubt

• Sugar for prototypal object pattern, also supports closure patterns:

• const px = Name.create(‘x’), py = Name.create(‘y’);

class Point extends Base {
constructor(x, y) {
super();
this[px] = x, this[py] = y;
this.r = function() { return Math.sqrt(x*x + y*y); }
}
get x() { return this[px]; }
get y() { return this[py]; }
proto_r() { return Math.sqrt(this[px] * this[px] +
this[py] * this[py]); }
equals(p) { return this[px] === p[px] &&
this[py] === p[py]; } mozilla
}

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(tentative syntax ahead, work in progress...)

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Triangle (the proto operator)

• Instead of var obj = {__proto__: base, a: 1, b: 2}, use
let obj = base <| {a: 1, b: 2}

• Works for other literal object forms:
let arr = base <| [p, q, r]
let fun = base <| function (...args) { ... }
let re = base <| /(w+)s+(w)+/g

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The monocle-mustache operator

• Inspired by PrototypeJS’s Object.extend

base.{a:1, b:2} // warning: updates base

• Copies all “own” right-hand-side properties (including private names) to base

• Should it generate a fresh value instead of mutating?

let obj = base.{a:1, b:2}

• Or if we want Prototype-style update, should it look like an assignment op?

base .= {a:1, b:2}
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Class pattern using triangle-monocle-mustache

• const px = Name.create(‘x’), py = Name.create(‘y’);

let Point = Base <| function (x, y) {
super();
this[px] = x, this[py] = y;
this.r = function() { return Math.sqrt(x*x + y*y); }
}.prototype.{
get x() { return this[px]; },
get y() { return this[py]; },
proto_r() { return Math.sqrt(this[px] * this[px] +
this[py] * this[py]); },
equals(p) { return this[px] === p[px] &&
this[py] === p[py]; }
}.constructor.{
allPoints: [] // class “static” property
} mozilla

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Not yet in Harmony: arrow function syntax

• Arrow function syntax, instead of λ, ƒ, or # (want to save # for later)

• Just like CoffeeScript: let identity = (x) -> x

• Expression body: const square = (x) -> (x * x)

• Statement body: let countUsed = (str) -> {
if (str in usedWords)
usedWords[str]++;
else
usedWords[str] = 1;
}

• Fat arrow too: callback = (msg) => ( this.vmail.push(msg) )

• Binding forms: let f() -> “writable”
const K() -> “readonly” mozilla

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Not yet in Harmony: block lambda revival

• Inspired by Smalltalk via Ruby

let empty = {||}; // no need for space between bars

assert(empty() === undefined);
assert(typeof empty === "function"); // native and implements [[Call]]
assert(empty.length === 0);

let identity = {|x| x}; // completion is return value

assert(identity(42) === 42);
assert(identity.length === 1);

let a = [1, 2, 3, 4];
let b = a.map {|e| e * e} // paren-free call with block is
// idiomatic control structure so
// no semicolon at end
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print(b); // [1, 4, 9, 16]

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More block lambda revival

• Paren-free calls, control effects: you know you want it...

b = a.map {|e| // newline in block ok
e * e * e} // newline after ends call

function find_first_odd(a) {
a.forEach { |e, i|
if (e & 1) return i; } // returns from function
return -1;
}

function escape_return() {
return {|e| return e};
}
b = escape_return();
try { b(42); } catch (e) {} // error, return from
// inactive function
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Good news

• ES.next is being drafted

• It has many usability and be-a-better-compiler-target improvements already

• Prototyping in SpiderMonkey and V8 is ongoing, so we’ll actually implementor-
and user-test before ﬁnalizing the speciﬁcation

• Even if we cut a few things -- still good progress

• Help wanted on the implementor- and user-testing fronts

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Languages targeting JS today
• CoffeeScript Family (& Friends): CoffeeScript Coco Parsec Contracts.coffee Uberscript ToffeeScript JS11 Kaffeine Jack move

• JavaScript Parsers and Extensions: Narcissus Traceur es-lab qfox reflect.js bdParse parse-js ZeParser

• Javascript Optimizers: Closure UglifyJS

• Security enforcing JavaScript: Caja ADsafe FBJS Jacaranda etc.

• Static or optional typing: Dart JavaScript++ SafeJS MileScript Mascara Roy

• Synchronous to Asynchronous JavaScript Compilers (CPS): Streamline.js mobl StratifiedJS NarrativeJS jwacs Jscex TameJS

• JavaScript Language Extensions: ContextJS Objective-J JS2 jangaroo Flapjax jLang RestrictMode TIScript

• Ruby: HotRuby rb2js RubyJS Red Quby Opal 8ball

• Python: PYXC-PJ Pyjamas Pyjs Skulpt PyCow PyvaScript

• Java: GWT Java2Script j2js

• Scala: scalagwt

• C#, .NET: jsc JSIL Script# Prefix

• Lisp, Scheme: BiwaScheme ClojureScript clojurejs EdgeLisp Fargo MobyScheme nconc Parenscript Ralph scheme2js Scriptjure Sibilant Spock

• OCaml: Ocamljs O'Browser Js_of_ocaml

• Haskell: ghcjs jmacro

• Smalltalk: Amber Clamato SilverSmalltalk LivelyKernel

• C/C++: Emscripten mala Clue

• Basic: NS Basic/App Studio, qb.js

• Multitarget: Haxe Fantom LZX Clue

•

•
Tierless languages (produce both client & server): Fun Ur WebSharper mobl E Sugar Opa

Visual, Blocks-based Languages: Waterbear JsMorphic ScriptBlocks
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• Others: Oia Quixe Gnusto Logo p2js Reb2Static RPN phype OP4JS jsForth wForth

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Demos

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Emscripten [Alon Zakai]

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RiverTrail: Parallel JS

• A ParallelArray library, like typed arrays but immutable.

• map, reduce, combine, ﬁlter, partition, scan, scatter -- all produce fresh
ParallelArray results

• Relies on associativity to parallelize arithmetic operations (this does inject
some f.p. non-determinism).

• A Firefox add-on that runs a Narcissus-based JS-to-OpenCL compiler over
ParallelArray code

• Source: github.com/RiverTrail/RiverTrail (user id should’ve been IntelLabs)

• Demo code contains a "DO NOT use strict”; directive! mozilla

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RiverTrail demo sample code

• the ParallelArray constructor builds on typed arrays:

NBody.private.initVel = new Array(numBodies);

NBody.private.initVelTA = new Float32Array(numBodies * 4);

var initAsteroidPos = new Array(50);

for (i = 0; i < 50; i++) {
initAsteroidPos[i] = new ParallelArray([
NBody.private.posTA[i * 3 + 0], // x
NBody.private.posTA[i * 3 + 1],
NBody.private.posTA[i * 3 + 2],
]);
}
. . .
NBody.private.asteroidPos = new ParallelArray(Float32Array, initAsteroidPos);
. . .
NBody.private.vel = new ParallelArray(Float32Array, NBody.private.initVel);
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ParallelArray methods in action

• combine method is a workhorse (takes variable number of args)

"animateTickParallel": function animateTickParallel() {

// increment (+=) velocity by acceleration
var newVel = NBody.private.vel.combine(
1,
low_precision(NBody.bodyVelocityLoopified),
NBody.private.pos,
numBodies,
NBody.Constant.deltaTime,
NBody.Constant.epsSqr,
NBody.time,
NBody.private.asteroidPos
);
. . . mozilla

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River Trail [Intel Labs]

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Conclusions

• JS is everywhere, it’s evolving, and it will die hard

• JS is not the bad guy

• No world domination by (under-funded) force -- not Dr. Evil

• Developers have learned how to use it well

• More like the good guy in the wrong place at the wrong time

• Bruce Willis in the Die Hard series...

• or current inspiration: classic Wesley Snipes mozilla

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Always bet on JS
• First they said JS couldn’t be useful
for building “rich Internet apps”

• Then they said it couldn’t be fast

• Then they said it couldn’t be ﬁxed

• Then it couldn’t do multicore/GPU

• Wrong every time!

• My advice: always bet on JS


Q&A

• @BrendanEich on twitter

• brendan@mozilla.org

• http://www.brendaneich.com/

• es-discuss@mozilla.org

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