Next-Generation JavaScript Language Tooling

Engineers4Engineers, http://engineers4engineers.org, Jun 28, 2013

Web applications written in JavaScript rapidly grow in size and complexity. Ensuring and tracking the quality of such large-scale complex applications is daunting, especially given the lack of proper language tooling. Even in 2013 our tricks of the trade are unfortunately still at the level of “missing semicolon” check.

In this presentation, a new trend in emerging composeable JavaScript language tools will be highlighted. Armed with these tools, a wide range of development and maintenance workflows, designed for the new breed of web applications, can be established: Simple static analysis, run-time complexity profiling, syntax augmentation/transformation, dynamic code analysis, as well as an end-to-end strategy for application testing.

Transcript

1. Next-Generation JavaScript Language Tooling @ariyahidayat June 28, 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. Composable Tools
13. 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
14. JavaScript in the Browser User Interface Browser Engine Graphics Stack Data Persistence Render Engine JavaScript Engine Networking I/O
15. JavaScript Engine Virtual Machine/ Interpreter Parser Runtime Source Syntax Tree Built-in objects, host objects, ... Fast and conservative
16. Parser var answer = 42 keyword equal sign identifier number Variable Declaration Identifier Literal Constant Tokenization → Tokens Parsing → Syntax Tree
17. { 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
18. Syntax Visualization http://esprima.org/demo/parse.html Try online! http://ariya.ofilabs.com/2012/04/javascript-syntax-tree-visualization-with-esprima.html
19. Execution Visualization http://int3.github.io/metajs/
20. Building Blocks → Tools https://speakerdeck.com/constellation/escodegen-and-esmangle-using-mozilla-javascript-ast-as-an-ir Parser Code Generator Source Syntax Tree Source Obvious examples: minifier, obfuscator, ...
21. Another Case: CoffeeScriptRedux JavaScript Parser Code Generator JavaScript Syntax Tree Generated JavaScript JavaScript Source CoffeeScript Source CoffeeScript Parser + Transformer
22. Consistency Convention Scalability Bring Your Own Tool (BYOT)
23. Inspection
24. 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, ...
25. 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
26. 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
27. 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
29. 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
30. Editing Autocomplete http://ariya.ofilabs.com/2013/03/javascript-editing-with-autocomplete.html http://esprima.org/demo/autocomplete.html Try online!
31. Type Annotation http://esprima.org/demo/autocomplete.html Try online!
32. Scope Visualization http://mazurov.github.io/eslevels-demo/
33. Scope and Highlight http://ariya.ofilabs.com/2013/04/javascript-variable-scope-and-highlight.html http://esprima.org/demo/highlight.html Try online!
34. Static Analysis
35. 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
36. 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
37. 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
38. 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
39. “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
40. Code Complexity http://jscomplexity.org/ if (true) "foo"; else "bar"; Control Flow Graph 6 edges 6 nodes 1 exit Cyclomatic Complexity = 2
41. 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); });
42. Continuous Monitoring of Complexity http://ariya.ofilabs.com/2013/05/continuous-monitoring-of-javascript-code-complexity.html
43. Complexity Visualization with Plato https://ariya.ofilabs.com/2013/01/javascript-code-complexity-visualization.html https://github.com/jsoverson/plato
44. Dynamic Analysis
45. 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/
46. 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
47. 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);
48. 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
49. 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
50. Buster.JS buster-istanbul Mocha mocha-istanbul Karma (née Testacular) built-in Intern built-in Grover built-in Istanbul vs Test Libraries
51. If you think JSLint hurts your feelings, wait until you use Istanbul. @davglass
52. ...I gave you my heart But the very next day you gave it away...
53. Performance Tweaks
54. 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
55. Measurement Confidence Accuracy Precision http://ariya.ofilabs.com/2013/06/javascript-timing-accuracy-vs-precision.html
56. 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
57. Fast = Enough? Alice Bob Chuck Dan ... Bob Alice Dan Chuck ... Address Book Application Sort How’s the speed? 2 ms to sort 10 contacts
58. 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 ???
59. Profile-Guide Optimization http://ariya.ofilabs.com/2011/11/matching-a-decimal-digit.html function isDigit(ch) { return '0123456789'.indexOf(ch) >= 0; } function isDigit(ch) { return ch !==' ' && '0123456789'.indexOf(ch) >= 0; } Letters Digits Spaces
60. 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
61. 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
62. 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!
63. 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
64. 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
65. Transformation
66. Source Transformation Parser Code Generator Source Syntax Tree Source In-place Modification Modified Source Regenerative Non-Destructive
67. 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
68. 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
69. Rename Refactoring Assistant http://ariya.ofilabs.com/2013/04/rename-refactoring-for-javascript-code.html http://esprima.org/demo/rename.html Try online!
70. 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
71. Parametrized Coding http://nornagon.github.com/scrubby/
72. Embrace the Future
73. Adaptive Tools Explicit Implicit Customize analysis options Define new sets of rules Infer from high-quality sample Observe the engineer’s behavior
74. Tools: The Final Frontier To boldly analyze what no man has analyzed before...
75. Thank You ariya.hidayat@gmail.com @AriyaHidayat ariya.ofilabs.com/highlights Credits: Some artworks are from http://openclipart.org speakerdeck.com/ariya