Supersonic JavaScript @ariyahidayat

First Things First, Steven Covey “The Big Rock” http://calendar.perfplanet.com/2013/javascript-performance-big-picture/

The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming. Computer Programming as an Art Knuth’s Turing Award lecture (1974)

Beyond checklists Global maximum

Short Function

Function = Expensive sortDepartment totalDepartementExpense totalEmployeesSalaries getEmployeeData OLD Wisdom

NEW movement Let the JavaScript engine figure out the best way to execute the functions.

Automatic Inlining function square(p) { return p * p; } function f(x) { var sum = 0; for (var i = 0; i < x; i++) sum += square(i); return sum; } function f(x) { var sum = 0; for (var i = 0; i < x; i++) sum += i * i; return sum; } http://ariya.ofilabs.com/2013/04/automatic-inlining-in-javascript-engines.html

Deferred Parsing To further reduce the time to first executed instruction, Chakra processes and emits bytecode only for functions that are about to be executed using a mechanism called deferred parsing. http://blogs.msdn.com/b/ie/archive/2012/06/13/advances-in-javascript-performance-in-ie10-and-windows-8.aspx

Lazy Parsing http://ariya.ofilabs.com/2012/07/lazy-parsing-in-javascript-engines.html function add(x, y) { return x + y; } function mul(x, y) { return x * y; } alert(add(40, 2)); Declare a function call add with the function body “{ return x + y; }”. Declare a function call mul with the function body “{ return x * y; }”. Call alert with the result of function add with 40 and 2 as the arguments. 1 2 Call function add. Hmm, it is not parsed yet. Call the real parser for “{ return x + y; }”. It accepts x and y as the arguments. The return value is a binary operation + of x and y.

Fixed Object Shape

WILD idea How to avoid any deoptimization in the JavaScript engine?

Shape Transition function Vehicle() { this.color = 'white'; this.speed = 0; } var car = new Vehicle(); car.color = 'black'; car.maker = 'BMW'; var motorbike = new Vehicle(); motorbike.wheels = ['front', 'back']; color speed color speed maker color speed wheels

(Optimized) Property Access console.log(car.color); Execute the generic property access Shape check Get the value from property #1 color speed

“Freeze” the Object Shape var universe = { answer: 42 }; // do something else universe.panic = false; var universe = { answer: 42, panic: true }; // do something else universe.panic = false; http://ariya.ofilabs.com/2012/02/javascript-object-structure-speed-matters.html

Avoid Conditional Transition var car = { color: 'blue' }; if (currentYear > 2015) car.backupCamera = new Camera(); var car = { color: 'blue', backupCamera: null }; if (currentYear > 2015) car.backupCamera = new Camera();

Garbage Handling

Minimize Object Construction https://www.youtube.com/watch?v=Vo72W1HWeFI var tick = new Date(); for (var i = 0, j = 0; i < 4e4; ++i){ var delta = new Date(); delta = delta - tick; tick = new Date(); j += delta; } var tick = Date.now(); for (var i = 0, j = 0; i < 4e4; ++i) { var delta = Date.now() - tick; tick = Date.now(); j += delta; }

GC Tracing on 56 ms: Scavenge 1.8 (36.0) -> 0.9 (36.0) MB, 2.8 ms 73 ms: Scavenge 1.8 (36.0) -> 0.9 (37.0) MB, 2.8 ms 89 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 1.0 ms 109 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 1.0 ms 126 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 0.9 ms 141 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 0.9 ms 159 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 0.9 ms 176 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 1.0 ms 192 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 0.9 ms 207 ms: Scavenge 1.9 (37.0) -> 0.9 (37.0) MB, 1.0 ms 54 ms: Scavenge 1.8 (36.0) -> 0.9 (36.0) MB, 2.9 ms 67 ms: Scavenge 1.8 (36.0) -> 0.9 (37.0) MB, 2.7 ms new Date( ) Date.now()

Memory Profiling https://developer.chrome.com/devtools/docs/javascript-memory-profiling

Performance Analysis

Timing Prepare the stopwatch Mark the start and the end Sampling Periodically check which function is being executed Tracing Track all function calls and exits http://ariya.ofilabs.com/2012/12/javascript-performance-analysis-sampling-tracing-and-timing.html

Profile Guided

No content

function isDigit(ch) { return (ch !== ' ') && '0123456789'.indexOf(ch) >= 0; } Fast Lane http://ariya.ofilabs.com/2013/07/profile-guided-javascript-optimization.html function isDigit(ch) { return '0123456789'.indexOf(ch) >= 0; } Shortcut

Object in a Set var valid_words = { 'foobar': true, 'bar': true, 'baz': true, 'quux': true }; function is_valid(word) { return valid_words.hasOwnProperty(word); } is_valid('fox'); // false http://ariya.ofilabs.com/2012/08/determining-objects-in-a-set-examples-in-javascript.html Dictionary Spell checker

Tiered Conditionals http://ariya.ofilabs.com/2012/08/determining-objects-in-a-set-examples-in-javascript.html function is_valid(word) { switch (word.length) { case 3: return word === 'bar' || word === 'baz'; case 4: return word === 'quux'; case 6: return word === 'foobar'; } return false; } Filter #1: length

Algorithmic Complexity

Fast = Enough? Alice Bob Chuck Dan ... Bob Alice Dan Chuck ... Sort How’s the speed? 2 ms to sort 10 contacts

Array.prototype.swap = function (i, j) { var k = this[i]; this[i] = this[j]; this[j] = k; } function sort(list) { var items = list.slice(0), swapped = false, p, q; for (p = 1; p < items.length; ++p) { for (q = 0; q < items.length - p; ++q) { if (items[q + 1] < items[q]) { items.swap(q, q + 1); swapped =true; } } if (!swapped) break; } return items; } Bubble Sort ???

Run-time Complexity http://ariya.ofilabs.com/2012/01/scalable-web-apps-the-complexity-issue.html Array.prototype.swap = function (i, j) { var k = this[i]; this[i] = this[j]; this[j] = k; } Array.prototype.swap = function (i, j) { Log({ name: 'Array.prototype.swap', lineNumber: 1, range: [23, 94] }); var k = this[i]; this[i] = this[j]; this[j] = k; }

No content

Final Words

tools and knowledge not rules and checklists

contextual profiling not microbenchmarks

T D D B D D

Thank You! shapesecurity.com @ariyahidayat And don’t forget to rate the talk