The Future of JavaScript Language Tooling

Silicon Valley Code Camp 2013:
http://www.siliconvalley-codecamp.com/Session/2013/the-future-of-javascript-language-tooling

It is inevitable that future JavaScript applications will grow to be more complex. Keeping the quality of such a complex system is far from trivial. Unfortunately, our JavaScript tools recently still move at a glacial speed. Many code analyzers scream at you when a semicolon is omitted, yet they are totally oblivious to a copy-paste mistake. This talk will discuss the development of emerging JavaScript language tooling designed to solve:
* code inspection: autocomplete, code outline
* static analysis: code metrics, API harness, cyclomatic complexity
* dynamic analysis: code coverage, execution tracing, run-time scalability
* source transformation: coding style, language extension (module, class, macro, …)

Transcript

1. The Future of JavaScript Language Tooling @ariyahidayat October 6, 2013
2. /usr/bin/whoami
3. Front-end development team Single-page applications
4. Static analysis Inspection Dynamic analysis Transformation
5. Every tool is open-source Tweak/customize/run with it! There are links (everywhere) to detailed articles/blog posts
6. Multi-Layer Defense
7. Defensive = Paranoid http://ariya.ofilabs.com/2012/12/quality-code-via-multiple-layers-of-defense.html
8. Placement of Layers Code Editor CI Server VCS Hooks Smoke Tests Pull Request Build Tasks
9. Feedback is Important Engineer Tools Feedback Cycle Boring Repetitive Time- consuming
10. Track Quality Metrics Application revision Execution time Baseline
11. Metrics Quadrant http://ariya.ofilabs.com/2012/11/optimization-journey-vs-destination.html
12. Be Reasonable “First Things First”, Steven Covey “The Big Rock”
13. Composable Tools
14. This is the Unix Philosophy Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface. Doug McIlroy, the inventor of Unix pipes and one of the founders of the Unix tradition
15. JavaScript in the Browser User Interface Browser Engine Graphics Stack Data Persistence Render Engine JavaScript Engine Networking I/O
16. JavaScript Engine Virtual Machine/ Interpreter Parser Runtime Source Syntax Tree Built-in objects, host objects, ... Fast and conservative
17. Parser var answer = 42 keyword equal sign identifier number Variable Declaration Identifier Literal Constant Tokenization → Tokens Parsing → Syntax Tree
18. { type: "Program", body: [ { type: "VariableDeclaration", declarations: [ { type: "VariableDeclarator", id: { type: "Identifier", name: "answer" }, init: { type: "Literal", value: 42, raw: "42" } } ], kind: "var" } ] } Syntax Tree Mozilla Parser API var answer = 42; Terms → ECMAScript 5.1 Specification https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API
19. Syntax Visualization http://esprima.org/demo/parse.html Try online! http://ariya.ofilabs.com/2012/04/javascript-syntax-tree-visualization-with-esprima.html
20. Execution Visualization http://int3.github.io/metajs/
21. Building Blocks → Tools Parser Code Generator Source Syntax Tree Source Obvious examples: minifier, obfuscator, ...
22. Another Case: CoffeeScriptRedux JavaScript Parser Code Generator JavaScript Syntax Tree Generated JavaScript JavaScript Source CoffeeScript Source CoffeeScript Parser + Transformer
23. Consistency Convention Scalability Bring Your Own Tool (BYOT)
24. Inspection
25. Syntax Validation http://ariya.ofilabs.com/2012/10/javascript-validator-with-esprima.html http://esprima.org/demo/validate.html Try online! Also available: Grunt plugin, Ant task, ...
26. Strict Mode Validator 'use strict'; block = { color: 'blue', height: 20, width: 10, color: 'red' }; Duplicate data property in object literal not allowed in strict mode http://ariya.ofilabs.com/2012/10/validating-strict-mode.html
27. Linter vs Validator Validator Linter Looks for specification violations Does not care about coding style Works well on generated/minified code Searches for suspicious pattern Warns on style inconsistencies Works well on hand-written code
28. Protection Layers, Again JUnit XML + Jenkins files=$(git diff-index --name- only HEAD | grep -P '\.js$') for file in $files; do esvalidate $file if [ $? -eq 1 ]; then echo "Syntax error: $file" exit 1 fi done Git Precommit Hook http://ariya.ofilabs.com/2012/03/git-pre-commit-hook-and-smoke-testing.html
30. Application Structure MyApp.create('MyApp.Person', { name: 'Joe Sixpack', age: 42, constructor: function(name) {}, walk: function(steps) {} run: function(steps) {} }); { objectName: 'MyApp.Person', functions: ['walk', 'run'], properties: ['name', 'age'] } Metadata
31. Editing Autocomplete http://ariya.ofilabs.com/2013/03/javascript-editing-with-autocomplete.html http://esprima.org/demo/autocomplete.html Try online!
32. Type Annotation http://esprima.org/demo/autocomplete.html Try online!
33. Scope Visualization http://mazurov.github.io/eslevels-demo/
34. Scope and Highlight http://ariya.ofilabs.com/2013/04/javascript-variable-scope-and-highlight.html http://esprima.org/demo/highlight.html Try online!
35. Static Analysis
36. Polluting Variables var height; // some fancy processing heigth = 200; Leaks to global test.js:3 heigth = 200; ^ LeakError: global leak detected: heigth https://github.com/kesla/node-leaky http://ariya.ofilabs.com/2012/11/polluting-and-unused-javascript-variables.html
37. Unused Variables var height; // some fancy processing heigth = 200; http://ariya.ofilabs.com/2012/11/polluting-and-unused-javascript-variables.html Declared but not used test.js height - on line 1 https://github.com/Kami/node-unused
38. Stray Logging function detect_console(code) { function check(node) { if (node.type === 'CallExpression') { if (node.callee.type === 'MemberExpression') { if (node.callee.object.name === 'console') { alert('console call at line', node.loc.start.line); } } } } var tree = esprima.parse(code, { loc: true }); estraverse.traverse(tree, { enter:check }); } var answer = 42; console.log(answer); http://ariya.ofilabs.com/2013/04/automagic-removal-of-javascript-logging.html
39. Nested Ternary Conditionals var str = (age < 1) ? "baby" : (age < 5) ? "toddler" : (age < 18) ? "child": "adult"; http://ariya.ofilabs.com/2012/10/detecting-nested-ternary-conditionals.html
40. “Boolean Trap” Finder Can you make up your mind? treeItem.setState(true, false); event.initKeyEvent("keypress", true, true, null, null, false, false, false, false, 9, 0); The more the merrier? Obfuscated choice var volumeSlider = new Slider(false); Double-negative component.setHidden(false); filter.setCaseInsensitive(false); http://ariya.ofilabs.com/2012/06/detecting-boolean-traps-with-esprima.html
41. Code Complexity http://jscomplexity.org/ if (true) "foo"; else "bar"; Control Flow Graph 6 edges 6 nodes 1 exit Cyclomatic Complexity = 2
42. Most Complex Function http://ariya.ofilabs.com/2013/05/continuous-monitoring-of-javascript-code-complexity.html var cr = require('complexity-report'), content = require('fs').readFileSync('index.js', 'utf-8'), list = []; cr.run(content).functions.forEach(function (entry) { list.push({ name: entry.name, value: entry.complexity.cyclomatic }); }); list.sort(function (x, y) { return y.value - x.value; }); console.log('Most cyclomatic-complex functions:'); list.slice(0, 6).forEach(function (entry) { console.log(' ', entry.name, entry.value); });
43. Continuous Monitoring of Complexity http://ariya.ofilabs.com/2013/05/continuous-monitoring-of-javascript-code-complexity.html
44. Complexity Visualization with Plato https://ariya.ofilabs.com/2013/01/javascript-code-complexity-visualization.html https://github.com/jsoverson/plato
45. Dynamic Analysis
46. Dynamic Code Coverage via Instrumentation var answer = 42; alert(answer); var __cov_l$4m7m$L464yvav5F$qhNA = __coverage__['hello.js']; __cov_l$4m7m$L464yvav5F$qhNA.s['1']++; var answer = 42; __cov_l$4m7m$L464yvav5F$qhNA.s['2']++; alert(answer); http://gotwarlost.github.io/istanbul/
47. Latent Trap of Statement Coverage function inc(p, q) { if (q == undefined) q = 1; return p + q/q; } assert("inc(4) must give 5", inc(4) == 5); Does not catch the missing code sequence http://ariya.ofilabs.com/2012/09/the-hidden-trap-of-code-coverage.html
48. Workaround: Explicit Path function inc(p, q) { if (q == undefined) return p + 1; return p + q/q; } assert("inc(4) must give 5", inc(4) == 5);
49. Branch Coverage http://ariya.ofilabs.com/2012/12/javascript-code-coverage-with-istanbul.html function inc(p, q) { if (q == undefined) q = 1; return p + q/q; } assert("inc(4) must give 5", inc(4) == 5); E = Else is not taken
50. Hard Thresholds on Code Coverage http://ariya.ofilabs.com/2013/05/hard-thresholds-on-javascript-code-coverage.html istanbul check-coverage --statement -5 --branch -3 --function 100
51. Buster.JS buster-istanbul Mocha mocha-istanbul Karma (née Testacular) built-in Intern built-in Grover built-in Istanbul vs Test Libraries
52. Code Coverage for Jasmine Tests Specs Karma Istanbul http://ariya.ofilabs.com/2013/10/code-coverage-of-jasmine-tests-using-istanbul-and-karma.html INFO [karma]: Karma v0.10.2 server started at http://localhost:9876/ INFO [launcher]: Starting browser PhantomJS INFO [PhantomJS 1.9.2 (Linux)]: Connected on socket N9nDnhJ0Np92NTSPGx-X PhantomJS 1.9.2 (Linux): Executed 1 of 1 SUCCESS (0.029 secs / 0.003 secs)
53. If you think JSLint hurts your feelings, wait until you use Istanbul. @davglass
54. ...I gave you my heart But the very next day you gave it away...
55. Performance Tweaks
56. http://ariya.ofilabs.com/2012/12/javascript-performance-analysis-sampling-tracing-and-timing.html 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
57. Measurement Confidence Accuracy Precision http://ariya.ofilabs.com/2013/06/javascript-timing-accuracy-vs-precision.html
58. What you write Optimized by the engine function test() { var a = 0, b = 0; for (var i = 0; i < 100; i++) { a += i; b += i * i; } return a; } function test() { var a = 0; for (var i = 0; i < 100; i++) { a += i; } return a; } Dead Code Elimination
59. Fast = Enough? Alice Bob Chuck Dan ... Bob Alice Dan Chuck ... Address Book Application Sort How’s the speed? 2 ms to sort 10 contacts
60. 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 ???
61. Profile-Guide Optimization function isDigit(ch) { return '0123456789'.indexOf(ch) >= 0; } function isDigit(ch) { return ch !==' ' && '0123456789'.indexOf(ch) >= 0; } Letters Digits Spaces http://ariya.ofilabs.com/2013/07/profile-guided-javascript-optimization.html
63. Object in a Set http://ariya.ofilabs.com/2012/08/determining-objects-in-a-set-examples-in-javascript.html var valid_words = { 'foobar': true, 'bar': true, 'baz': true, 'quux': true }; function is_valid(word) { return valid_words.hasOwnProperty(word); } is_valid('fox'); // false Dictionary Spell checker Alternatives: array lookup, switch case, prefix/suffix tree, perfect hash
64. Tiered Conditionals 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 http://ariya.ofilabs.com/2012/08/determining-objects-in-a-set-examples-in-javascript.html
65. Empirical Run-time Complexity 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; } http://esprima.org/demo/functiontrace.html Try online!
66. Run-time Analysis 0 250000 500000 0 500 1000 Calls to swap() Input Size http://ariya.ofilabs.com/2012/01/scalable-web-apps-the-complexity-issue.html
67. Execution Tracing http://ariya.ofilabs.com/2012/02/tracking-javascript-execution-during-startup.html https://gist.github.com/1823129 jQuery Mobile startup log 4640 function calls jquery.js 26 jQuery jquery.js 103 init undefined, undefined, [object Object] jquery.js 274 each (Function) jquery.js 631 each [object Object], (Function), undefined jquery.js 495 isFunction [object Object] jquery.js 512 type [object Object] jquery.mobile.js 1857 [Anonymous] jquery.mobile.js 642 [Anonymous] jquery.mobile.js 624 enableMouseBindings jquery.mobile.js 620 disableTouchBindings
68. Transformation
69. Source Transformation Parser Code Generator Source Syntax Tree Source In-place Modification Modified Source Regenerative Non-Destructive http://ariya.ofilabs.com/2013/06/javascript-source-transformation-non-destructive-vs-regenerative.html
70. String Literal Quotes [ { type: "Identifier", value: "console", range: [0, 7] }, { type: "Punctuator", value: ".", range: [7, 8] }, { type: "Identifier", value: "log", range: [8, 11] }, { type: "Punctuator", value: "(", range: [11, 12] }, { type: "String", value: "\"Hello\"", range: [12, 19] }, { type: "Punctuator", value: ")", range: [19, 19] } ] console.log('Hello') console.log("Hello") List of tokens http://ariya.ofilabs.com/2012/02/from-double-quotes-to-single-quotes.html
71. Style Formatter CodePainter Source Sample code Formatted Infer coding styles Indentation Quote for string literal Whitespace esformatter Source Formatted Style options Indentation Line breaks Whitespaces https://github.com/millermedeiros/esformatter
72. Rename Refactoring Assistant http://ariya.ofilabs.com/2013/04/rename-refactoring-for-javascript-code.html http://esprima.org/demo/rename.html Try online!
73. function f() { var j = data.length; console.log(j, 'items'); for (var i = 0; i < j; ++i) { var j$0 = data[i] * data[i]; console.log(j$0); // squares } } Lexical Block Scope function f() { let j = data.length; console.log(j, 'items'); for (let i = 0; i < j; ++i) { let j = data[i] * data[i]; console.log(j); // squares } } https://github.com/olov/defs New in ECMAScript 6 http://ariya.ofilabs.com/2013/05/es6-and-block-scope.html
74. Parametrized Coding http://nornagon.github.com/scrubby/
75. Embrace the Future
76. Adaptive Tools Explicit Implicit Customize analysis options Define new sets of rules Infer from high-quality sample Observe the engineer’s behavior
77. Tools: The Final Frontier To boldly analyze what no man has analyzed before...
78. Thank You ariya.hidayat@gmail.com @ariyahidayat ariya.ofilabs.com/highlights Credits: Some artworks are from http://openclipart.org speakerdeck.com/ariya