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Elements of Functional Programming in JS
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Adam Stankiewicz
May 27, 2014
Programming
2
160
Elements of Functional Programming in JS
Lightning talk from Meet.js Wrocław.
Adam Stankiewicz
May 27, 2014
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Transcript
Elements of Functional Programming in JavaScript
What is functional programming? No generally accepted definition, but: •
Style of building computer programs • Avoids state and mutable data • Functions as arguments and results
Benefits of functional programming • More concise, readable code •
Confident refactor, better reasoning • Better concurrency? • Performance (function inlining)
JS has some functional elements • First class functions •
Anonymous functions (lambdas) • ???
JS lacks many functional elements • Tail call optimization •
Pattern matching • Forced immutability (type system) • No standard methods for FP (IE <=8) ◦ Array#forEach, Array#map, Array#filter, etc...
Libraries for FP in JavaScript • Underscore • Lo-Dash •
Mout.js (for Node.js)
Short map syntax var characters = [ { 'id': 1,
'name': 'barney', 'age': 26 }, { 'id': 2, 'name': 'fred', 'age': 30 } ]; _.map(characters, function(c) { return c['name']; }) // ['barney', 'fred'] _.map(characters, 'name') // ['barney', 'fred']
Short filter syntax var characters = [ { 'id': 1,
'name': 'barney', 'age': 26 }, { 'id': 2, 'name': 'fred', 'age': 30 } ]; _.filter(characters, function(c) { return c.age == 30; }) // [{ 'id': 2, 'name': 'fred', 'age': 30 }] _.filter(characters, { age: 30 }) // [{ 'id': 2, 'name': 'fred', 'age': 30 }]
General pattern // function(e) { return e['foo']; } // 'foo'
_.sortBy(characters, 'name') // function(e) { return e['foo'] == bar; } // { 'foo': bar } _.every(characters, { 'name': 'barney' })
GroupBy var words = ['one', 'two', 'three'] _.groupBy(words, 'length'); //
{ '3': ['one', 'two'], '5': ['three'] }
IndexBy var users = [ { 'id': 100, 'name': 'Adam'
}, { 'id': 200, 'name': 'Ala' } ]; var indexedUsers = _.indexBy(users, 'id') indexedUsers[100] // { 'id': 100, 'name': 'Adam' } indexedUsers[200] // { 'id': 100, 'name': 'Ala' }
Find var users = [ { 'id': 100, 'name': 'Adam'
}, { 'id': 200, 'name': 'Ala' } ]; _.find(users, { 'id': 100 }); // { 'id': 100, 'name': 'Adam' }
max, min var characters = [ { 'name': 'barney', 'age':
26 }, { 'name': 'fred', 'age': 30 } ]; _.max(characters, 'age') // { 'name': 'fred', 'age': 30 } _.min(characters, 'age') // { 'name': 'barney', 'age': 26 }
reduce var numbers = [1, 2, 3]; _.reduce(numbers, function(sum, element)
{ return sum + element }); // 6
Composing functions var characters = [ { 'name': 'barney', 'age':
26 }, { 'name': 'fred', 'age': 30 }, // ... ]; var ages = _.map(characters, 'age'); // [26, 30] _.reduce(ages, function(a, b) { return a + b }); // [56]
Composing functions var characters = [ { 'name': 'barney', 'age':
26 }, { 'name': 'fred', 'age': 30 }, // ... ]; _(characters) .map('age') .reduce(function(a, b) { return a + b; });
Composing functions var characters = [ { 'name': 'barney', 'age':
26 }, { 'name': 'fred', 'age': 30 }, // ... ]; _(characters) .map('age') .reduce(function(a, b) { return a + b; });
Other features • Set operations (difference, union, intersection) • every,
some, reject, countBy, contains • clone, extend, defaults, merge, mapValues • delay, defer, memoize, once, throttle • now, random, uniqueId, template
Promises A+ • Pattern for running async code • Allows
for return in callbacks • Safely handles exceptions in callbacks • Allows for try/catch -like behavior • Chaining of callbacks, parallel execution promise.then(onSuccess, onFailure)
Promises A+ $http.get('/users/1').then(function(user) { return $http.get("/users/posts"); }).then(function(post) { return render(post);
}).catch(function(reason) { console.log(reason); });
Dzięki