Functional Programming using underscore.js

Transcript

1. Functional Programming using Underscore.js othree @ OSDC 2013
2. me • @othree • https://blog.othree.net
3. me • PhD Candidate • Front End Engineer • On the way learning good from functional programming languages
4. Function of Functional Language • Pure function • First class citizen • Higher order function • ...
5. Pure Function • Side effect free • Same input, same output • ex: trigonometric functions
6. First Class Citizen • Function like variable • ex: function expression var f = function () { /*...*/ };
7. Higher Order Function • Function takes or return functions • ex: event listener
8. http://www.flickr.com/photos/78428166@N00/6036104277/
9. Take a Look Examples from ‘Pure, functional JavaScript’ http://cjohansen.no/talks/2012/sdc-functional/
10. [ { name: 'Gates', gender: 'M', org: 'M$' }, { name: 'Peter' gender: 'M', org: 'Hㄒㄈ' } ]
11. "Mentioned by Gates, Peter, Jobs"
12. var str = "Mentioned by "; for (var i = 0, l = tweeps.length; i < l; ++i) { str += tweeps[i].name; if (i < tweeps.length - 1) { str += ", "; } }
13. [ { name: 'Gates', gender: 'M', org: 'M$' }, { name: 'Peter' gender: 'M', org: 'Hㄒㄈ' } ]
14. [ 'Gates', 'Peter' ]
15. var names = []; for (var i = 0, l = tweeps.length; i < l; ++i) { names.push(tweeps[i].name); }
16. var str = "Mentioned by " + names.join(", ");
17. var names = tweeps.map(function (tweep) { return tweep.name; });
18. var names = tweeps.map(function (t) { return t.name; });
19. var str = "Mentioned by " + tweeps.map(function (t) { return t.name; }).join(", ");
20. function prop(name) { return function (object) { return object[name]; }; }
21. var str = "Mentioned by " + tweeps.map(prop("name")).join(", ");
22. Case 2
23. [ { getSummary: function () { return { text: 'Summaries', html: '<p>Summaries</p>' }; } }, { getSummary: function () { return {text: 'Summaried'}; } }, ... ]
24. <div> <p>Summaries</p> <p>Summaried</p> <p>Summary</p> </div>
25. buildSummary: function () { var div = document.createElement("div"), p; for (var i = 0, l = this.components.length; i < l; ++i) { p = document.createElement("p"); p.innerHTML = this.components[i].getSummary().text; div.appendChild(p); } return div; }
26. DOM functions
27. var ul = cull.dom.el("ul"); ul.nodeType === 1 // true https://github.com/culljs/dome/
28. var ul = cull.dom.el("ul", { className: "bands" }); // var li = cull.dom.el("li", "Execration"); var ul = cull.dom.el("ul", { className: "bands" }, li);
29. var ul = cull.partial(cull.dom.el, "ul"); var li = cull.partial(cull.dom.el, "li");
30. ["a", "br", "code", "div", ...].forEach(function (tagName) { cull.dom.el[tagName] = cull.partial(cull.dom.el, tagName); }); // ["a", "br", "code", "div", ...].forEach(function (tagName) { root[tagName] = cull.partial(cull.dom.el, tagName); });
31. http://www.flickr.com/photos/jackhynes/519904699/
32. buildSummary: function () { return div(this.components.map(function (component) { return p(component.getSummary().text); })); }
33. buildSummary: function () { return div(this.components.map(function (component) { return p(component.getSummary().text); })); } 1
34. buildSummary: function () { return div(this.components.map(function (component) { return p(component.getSummary().text); })); } 1 2
35. buildSummary: function () { return div(this.components.map(function (component) { return p(component.getSummary().text); })); } 1 2 3
36. buildSummary: function () { return div(this.components. map(function (component) { return component.getSummary(); }).map(function (summary) { return summary.text; }).map(function (text) { return p(text); })); }
37. function func(name) { return function (object) { return object[name](); }; }
38. buildSummary: function () { return div(this.components. map(func("getSummary")). map(function (summary) { return summary.text; }).map(function (text) { return p(text); })); }
39. buildSummary: function () { return div(this.components. map(func("getSummary")). map(prop("text")). map(function (text) { return p(text); })); }
40. buildSummary: function () { return div(this.components. map(func("getSummary")). map(prop("text")). map(p)); }
41. var summarize = compose([p, prop("text"), func("getSummary")]);
42. var callGetSummary = func("getSummary"); var getText = prop("text"); var summarize = compose([p, getText, callGetSummary]); // summarize(obj); // => callGetSummary(obj) // => getText(callGetSummary(obj)) // => p(getText(callGetSummary(obj)))
43. buildSummary: function () { var summarize = compose([p, prop("text"), func("getSummary")]); return div(this.components.map(summarize)); }
44. var summarize = compose([p, prop("text"), func("getSummary")]); // ... buildSummary: function () { return div(this.components.map(summarize)); }
45. http://www.flickr.com/photos/guerson/5630633727/
46. Functional Programming in JavaScript
47. Native • forEach • map/reduce • filter
48. Functional JavaScript • by Oliver Steele at 2007 • First functional JavaScript Library I know
49. Underscore.js • by Jeremy Ashkenas from DocumentCloud • “Underscore is a utility-belt library for JavaScript that provides a lot of the functional programming support”
50. Lo-Dash • Will talk later
51. cull.js • by Christian Johansen and Magnar Sveen • “Cull is a toolbelt for writing functional javascript.” • Used in the examples above https://github.com/culljs/culljs
52. LiveScript & prelude.ls • by George Zahariev • A new compile to JavaScript language fork from Coco • Stay in this room until tomorrow, Mindos have a talk about LiveScript
53. GHCJS • by Hamish Mackenzie, Victor Nazarov, Luite Stegeman • Haskell to JavaScript compiler
54. Underscore.js • compose • map/reduce • filter • pluck
55. var str = "Mentioned by " + tweeps.map(prop("name")).join(", ");
56. var str = "Mentioned by " + _.reduce( _.map(tweeps, function (t) { return t.name; }), function (memo, name, i) { return (i == 0) ? name : memo + ', ' + name; }, '' );
57. var str = "Mentioned by " + _(tweeps) .chain() .map(function (t) { return t.name; }) .reduce(function (memo, name, i) { return (i == 0) ? name : memo + ', ' + name; }, '') .value();
58. var str = "Mentioned by " + _(tweeps) .map(function (t) { return t.name; }) .join(', ');
59. var str = "Mentioned by " + _(tweeps).pluck('name').join(', ');
60. Still Not Enough • curry, partial • prop, func from above example
61. Lo-Dash
62. Functional Programming using Underscore.js othree @ OSDC 2013.1
63. Functional Programming using Underscore.js Lo-Dash othree @ OSDC 2013.1
64. -
65. @
66. @ -
67. @ -
68. What is Lo-Dash • Underscore.js fork by John-David Dalton, Kit Cambridge, and Mathias Bynens
69. Difference • Better performance • Robust result • Larger file size • AMD supports • Auto chain • More power: cloneDeep, partial, result...
70. _.partial var greet = function(greeting, name) { return greeting + ' ' + name; }; var hi = _.partial(greet, 'hi'); hi('moe'); // ! 'hi moe' http://lodash.com/docs#partial
71. _.result var object = { 'cheese': 'crumpets', 'stuff': function () { return 'nonsense'; } }; _.result(object, 'cheese'); // ! 'crumpets' _.result(object, 'stuff'); // ! 'nonsense' http://lodash.com/docs#result
72. With Lo-Dash
73. var summarize = compose([p, prop("text"), func("getSummary")]); // ... buildSummary: function () { return div(map(summarize), this.components); }
74. var summarize = _.compose( p, _.partialRight(_.result, 'name'), _.partialRight(_.result, 'getSummary') ); // ... buildSummary: function () { return div(_.map(this.components, summarize)); }
75. Performance?
76. Bad..
77. http://jsperf.com/for-vs-foreach/71
78. http://jsperf.com/for-vs-foreach/71
79. • Take benefits from functional programming • Not change everything to functional • Library helps, ex: lo-dash
80. References Further Readings
81. http://interglacial.com/hoj/hoj.html
82. http://cjohansen.no/talks/2012/sdc-functional/
83. http://kitcambridge.be/blog/say-hello-to-lo-dash/
84. http://www.slideshare.net/ihower/fp-osdc2012v2
85. http://shop.oreilly.com/product/9781593272821.do
86. http://shop.oreilly.com/product/0636920028857.do
87. http://shop.oreilly.com/product/0636920028857.do N ot Yet Released
88. Questions? http://www.flickr.com/photos/roman/5610736/