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Introduction Understanding the Dynamics of JavaScript JavaScript Sylvain Lebresne, Gregor Richards, Johan Ostlund, Tobias Measurements Wrigstad, Jan Vitek Purdue University Results July 6, 2009 Conclusions 1 / 28 2 / 28 Introduction

  1. Introduction Understanding the Dynamics of JavaScript JavaScript Sylvain Lebresne, Gregor Richards, Johan ¨ Ostlund, Tobias Measurements Wrigstad, Jan Vitek Purdue University Results July 6, 2009 Conclusions 1 / 28 2 / 28 Introduction — The Significance of JavaScript 1 Introduction ◮ Language of “Web 2.0” ◮ Dynamic language used for large, structured web programs ◮ Supplanting Java applets, Flash 1 JavaScript is also known as ECMAScript, JScript 3 / 28 4 / 28

  2. Introduction — Motivation Introduction — JavaScript and Types ◮ Understand real-world patterns used in dynamic languages ◮ Extremely dynamic, flexible object system ◮ Do dynamic languages beget untypable code? ◮ No static notion of type ◮ Potential for type analysis of JavaScript ◮ But is the dynamicity used? ◮ What patterns in JavaScript could be recreated in a static context 5 / 28 6 / 28 JavaScript — The Language JavaScript ◮ Imperative, object-oriented ◮ Minimalistic standard library ◮ 3rd-party libraries abstract the type system (Prototype.js, jQuery, Ext) 7 / 28 8 / 28

  3. JavaScript — Prototypes JavaScript — Terminology ◮ Constructors have a prototype field, the prototype of objects ◮ Objects have a prototype, which is another object created by the constructor: X.prototype is not the ◮ Field lookup looks in the object itself, then its prototype prototype of X , but the prototype of objects created by X ◮ Prototype chains act like subtype relationships ◮ The prototype of an object is accessible in many implementations by the field proto 9 / 28 10 / 28 JavaScript — Prototypes Example Questions function List(v, n) { this.v = v; this.n = n; } ◮ How often do prototypes change after first instantiation? List ◮ How often do prototype chains change after first instantiation? ◮ How often are entirely new fields or methods added to live List.prototype objects? ◮ What is the object-to-prototype ratio? prototype ◮ How complex/deep are prototype hierarchies? ◮ Do JavaScript programs make use of type introspection? ◮ What is the ratio of message sends and field updates? List.prototype.map return new List(f(this.v), this.n ? this.n.map(f) : null); } 11 / 28 12 / 28 List List.prototype prototype List.prototype.map map List List prototype List.prototype prototype l List.prototype l List.prototype.map List.prototype.map map map map List prototype List.prototype l

  4. Measurements — Dirtiness ◮ Primary measurement is “dirtiness” of objects ◮ Dirtying actions: Measurements ◮ Addition or deletion of a property ◮ Update of a method ◮ Update of the prototype field ◮ Intuition: ◮ “Clean” objects are nearly statically typable ◮ “Dirty” objects use dynamic features ◮ Update of a field explicitly ignored 13 / 28 14 / 28 Measurements — Test Cases Results — Objects ◮ SunSpider tests ◮ Popular for benchmarking JavaScript implementations ◮ Results broken down by objects, in these categories: ◮ “(...) avoids microbenchmarks, and tries to focus on the kinds ◮ Regular objects : objects created by new (and array literals.) of actual problems developers solve with JavaScript today, ◮ Constructors : functions used to create regular objects. (...)” ◮ Functions : functions that are not used as a constructor. ◮ Real web pages ◮ Prototypes : objects created as prototypes of functions. ◮ Amazon, Basecamp, Facebook, Gmail, LivelyKernel, NASA ◮ Random walk (normal web surfing activity) 15 / 28 16 / 28

  5. Results — Object Dirtiness Results — Object Dirtiness Regular Objects Prototypes Constructors Other Functions Objects 3d-cube 20491 (0.02%) 23 (0%) 1 (0%) 14 (0%) 20529 (0.02%) Regular Objects Prototypes Constructors Other Functions Objects 3d-raytrace 10742 (0.61%) 36 (0%) 3 (0%) 25 (0%) 10806 (0.61%) 3d-cube 20491 (0.02%) 23 (0%) 1 (0%) 14 (0%) 20529 (0.02%) binary-trees 42072 (0%) 11 (0%) 1 (0%) 2 (0%) 42086 (0%) 3d-raytrace 10742 (0.61%) 36 (0%) 3 (0%) 25 (0%) 10806 (0.61%) v8-crypto 1076 (44%) 140 (2.86%) 5 (20%) 127 (0%) 1348 (35.5%) binary-trees 42072 (0%) 11 (0%) 1 (0%) 2 (0%) 42086 (0%) v8-deltablue 22854 (0%) 87 (1.15%) 15 (73.33%) 64 (3.12%) 23020 (0.07%) v8-crypto 1076 (44%) 140 (2.86%) 5 (20%) 127 (0%) 1348 (35.5%) v8-raytrace 399685 (0.02%) 361 (1.94%) 18 (100%) 335 (5.37%) 400399 (0.03%) v8-deltablue 22854 (0%) 87 (1.15%) 15 (73.33%) 64 (3.12%) 23020 (0.07%) v8-richards 3000 (0%) 46 (0%) 7 (0%) 31 (0%) 3084 (0%) v8-raytrace 399685 (0.02%) 361 (1.94%) 18 (100%) 335 (5.37%) 400399 (0.03%) amazon 31589 (21.6%) 20909 (0%) 1 (100%) 20750 (4.9%) 73249 (10.7%) v8-richards 3000 (0%) 46 (0%) 7 (0%) 31 (0%) 3084 (0%) basecamp 4381 (5.2%) 1796 (0.4%) 0 (0%) 1663 (0%) 7840 (3%) amazon 31589 (21.6%) 20909 (0%) 1 (100%) 20750 (4.9%) 73249 (10.7%) facebook 72231 (28.5%) 22692 (1.4%) 167 (69.5%) 22407 (13.1%) 117497 (20.4%) basecamp 4381 (5.2%) 1796 (0.4%) 0 (0%) 1663 (0%) 7840 (3%) gmail 55833 (24%) 11140 (0.06%) 1899 (98.8%) 8338 (40.4%) 77210 (24.1%) facebook 72231 (28.5%) 22692 (1.4%) 167 (69.5%) 22407 (13.1%) 117497 (20.4%) livelykernel 316717 (7.1%) 70036 (0%) 1 (0%) 69845 (0.01%) 456599 (4.9%) gmail 55833 (24%) 11140 (0.06%) 1899 (98.8%) 8338 (40.4%) 77210 (24.1%) nasa 93989 (3.1%) 13853 (2.7%) 24 (4.2%) 13352 (0.06%) 121218 (2.7%) livelykernel 316717 (7.1%) 70036 (0%) 1 (0%) 69845 (0.01%) 456599 (4.9%) random 47921 (16.4%) 12680 (0.15%) 189 (55%) 12338 (0.4%) 73128 (11%) nasa 93989 (3.1%) 13853 (2.7%) 24 (4.2%) 13352 (0.06%) 121218 (2.7%) random 47921 (16.4%) 12680 (0.15%) 189 (55%) 12338 (0.4%) 73128 (11%) ◮ Regular object dirtiness usually due to “optional” fields or ◮ Prototypes are dirty if modified after the first instance is object literals created ◮ v8-crypto : bignums constructor does not always create some ◮ Adding fields to Object.prototype and String.prototype fields; created instead by later functions such as fromInt ◮ v8-crypto : “static” fields zero and one ◮ v8-raytrace : optional shader function added to some (but not all) objects 17 / 28 18 / 28 Results — Object Dirtiness Results — Object Dirtiness Regular Objects Prototypes Constructors Other Functions Objects 3d-cube 20491 (0.02%) 23 (0%) 1 (0%) 14 (0%) 20529 (0.02%) function BigNum(val) { ... } 3d-raytrace 10742 (0.61%) 36 (0%) 3 (0%) 25 (0%) 10806 (0.61%) binary-trees 42072 (0%) 11 (0%) 1 (0%) 2 (0%) 42086 (0%) BigNum.ZERO = new BigNum(0); v8-crypto 1076 (44%) 140 (2.86%) 5 (20%) 127 (0%) 1348 (35.5%) BigNum.ONE = new BigNum(1); v8-deltablue 22854 (0%) 87 (1.15%) 15 (73.33%) 64 (3.12%) 23020 (0.07%) v8-raytrace 399685 (0.02%) 361 (1.94%) 18 (100%) 335 (5.37%) 400399 (0.03%) BigNum.prototype.add = function(to) { ... } v8-richards 3000 (0%) 46 (0%) 7 (0%) 31 (0%) 3084 (0%) amazon 31589 (21.6%) 20909 (0%) 1 (100%) 20750 (4.9%) 73249 (10.7%) basecamp 4381 (5.2%) 1796 (0.4%) 0 (0%) 1663 (0%) 7840 (3%) facebook 72231 (28.5%) 22692 (1.4%) 167 (69.5%) 22407 (13.1%) 117497 (20.4%) function BigNum(val) { ... } gmail 55833 (24%) 11140 (0.06%) 1899 (98.8%) 8338 (40.4%) 77210 (24.1%) livelykernel 316717 (7.1%) 70036 (0%) 1 (0%) 69845 (0.01%) 456599 (4.9%) BigNum.prototype.add = function(to) { ... } nasa 93989 (3.1%) 13853 (2.7%) 24 (4.2%) 13352 (0.06%) 121218 (2.7%) BigNum.ZERO = new BigNum(0); random 47921 (16.4%) 12680 (0.15%) 189 (55%) 12338 (0.4%) 73128 (11%) BigNum.ONE = new BigNum(1); ◮ Emulation of class-based behavior common, further investigation needed 19 / 28 20 / 28

  6. Results — Constructors and Functions Results — Dirtiness Sources Object.prototype.inherits = function(shuper) { function Inheriter() {} Inheriter.prototype = shuper.prototype; ◮ Results broken down by source of dirtiness this.prototype = new Inheriter(); ◮ Method addition this.superConstructor = shuper; } ◮ Method update function List(...) = { ... } ◮ Field addition function ColorList(...) = { ◮ Prototype update ColorList.superConstructor.call(this, ...); ◮ Deletion ... } ColorList.inherits(List); 21 / 28 22 / 28 Results — Dirtiness Sources Results — Dirtiness Sources Deletions Meth. add. Field add. 3d-cube 3d-cube 3d-raytrace 3d-raytrace binary-trees binary-trees v8-crypto v8-crypto v8-deltablue v8-deltablue v8-raytrace v8-raytrace v8-richards v8-richards amazon amazon basecamp basecamp facebook facebook gmail gmail livelykernel livelykernel nasa nasa random random 0 1000 2000 3000 4000 5000 6000 7000 0 5000 10000 15000 20000 25000 23 / 28 24 / 28

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