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Forgotten funky functions http://jakobm.com @jakobmattsson

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Startup hedge fund?

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Far from perfect and not for everything* or everyone * no, really

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Smorgasbord

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1 Function => Function 2 Meta-programming 3 There is no class

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1 Function => Function

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Error handling You just divided by zero, didn’t you?

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get('/users/123', function(err, response) { if (err) { cb(err); return; } cb(null, response.firstName); });

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get('/users/123', p(cb, function(response) { cb(null, response.firstName); }));

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var propagate = function(onErr, onSuccess) { return function(err) { if (err) { return onErr(err); } else { var slice = Array.prototype.slice; var rest = slice.call(arguments, 1); return onSuccess.apply(this, rest); } }; };

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propagate = (onErr, onSucc) -> (err, rest...) -> if err then onErr(err) else onSucc(rest...) CoffeeScript ConferenceScript

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(function, function) => function

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(function, function) => function Need to solve a JavaScript problem? Add on one more function!

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var once = function(f) { var called = false; var result = null; return function() { if (!called) { result = f.apply(this, arguments); called = true; } return result; }; };

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var initOnce = once(init); initOnce(); initOnce(); initOnce(); // only called once...

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var stateful = function(f) { var state = {}; return function() { var slice = Array.prototype.slice; var args = slice.call(arguments, 0); return f.apply(this, [state].concat(args)); }; };

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var once = stateful(function(state, f) { return function() { if (!state.called) { state.result = f.apply(this, arguments); state.called = true; } return state.result; }; });

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1 Function => Function call apply arguments slice bind …and closures!

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2 Meta-programming

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var fullName = function(firstName, lastName) { return firstName + " " + lastName; }; fullName('Jakob', ’Mattsson’); // ”Jakob Mattsson”

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var fullName = function(firstName, lastName) { return firstName + " " + lastName; }; fullName('Jakob', ’Mattsson’); var fullName2 = argsAsObject(fullName); fullName2({ firstName: ’Jakob', lastName: ’Mattsson' });

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// foo.com/fullName2?firstName=J&lastName=M funcs[req.path](req.query);

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var argNames = function(f) { var reg = /\(([\s\S]*?)\)/; var head = reg.exec(f)[1]; var argCands = head.split(/[ ,\n\r\t]+/); var names = argCands.filter(function(x) { return x; }; return names; };

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var argsAsObject = function(f) { var names = argNames(f); return function(args) { var argValues = names.map(function(name) { return args[name]; }); return f.apply(this, argValues); }; };

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var fullName2 = argsAsObject(fullName); fullName2({ firstName: ’Jakob', lastName: ’Mattsson' });

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fullName = renameArgs(fullName, [ ’first_name’, ’last_name’ ]); var fullName2 = argsAsObject(fullName); fullName2({ first_name: ’Jakob', last_name: ’Mattsson' });

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var renameArgs = function(__uniq, argNames) { var parts = [ "(function(", argNames.join(', ') ") { " "return __uniq.apply(this, arguments);" "});" ]; return eval(parts.join('')); };

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fullName2({ firstName: 'Jakob', lastName: 'Mattsson' }); var fullName = spreadArguments(fullName2, [ 'firstName', 'lastName' ]); fullName('Jakob', 'Mattsson'); // => 'Jakob Mattsson' Challenge!

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2 Meta-programming eval Function.toString()

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3 There is no class

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new MyConstructor MyConstructor.prototype … and what about types?? Original JavaScript

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class constructor extend(s) super CoffeeScript and ECMAScript 6

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Everyone forgot Object.create

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var Animal = { greet: function() { return this.speak() + ” says ” + this.name; } }; var Dog = Object.create(Animal); Dog.speak = function() { return ”woof”; }; var zelda = Object.create(Dog); zelda.name = ”zelda”; console.log(zelda.greet());

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But overloading?!

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var Animal = { greet: function() { return this.speak() + " says " + this.name; } }; var Dog = createAndInit(Animal, { speak: function(superSpeak) { return "woof"; }, greet: function(superGreet) { return superGreet() + ", who is a dog"; } });

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var createAndInit = function(source, props){ var slice = Array.prototype.slice; var newObj = Object.create(source); Object.keys(props).forEach(function(propName){ newObj[propName] = function(){ var zup = source[propName]; var boundZuper = zup ? zup(this) : null; var newFunc = props[propName]; var args = slice.call(arguments, 0); var allArgs = [boundZuper].concat(args); return newFunc.apply(this, allArgs); }; }); return newObj; };

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So what is Object.create really?

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Object.create = function(x) { function F() {} F.prototype = x; return new F(); }; new MyConstructor MyConstructor.prototype

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"I have been writing JavaScript for 14 years now (...). The super idea is fairly important in the classical pattern, but it appears to be unnecessary in the prototypal and functional patterns. I now see my early attempts to support the classical model in JavaScript as a mistake.” http://www.crockford.com/javascript/inheritance.html

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3 There is no class Object.create

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Forgotten funky functions http://jakobm.com @jakobmattsson