5 things I learned about coffeescript

(in my year with it)

Wednesday, June 5, 13

Dean Hudson, @deaneroSenior Engineer, Super Secret Music Start Up

(and hiring!)

Who Am I?

Wednesday, June 5, 13

1. coffee -cp

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dean@hdh:~/Devel/coffee$ coffee --help

Usage: coffee [options] path/to/script.coffee -- [args]

[...] -c, --compile compile to JavaScript and save as .js files -p, --print print out the compiled JavaScript [...]

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to see that this...

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qsort = (ar) -> return ar unless ar.length > 1 pivot = ar.pop() less = [] more = [] for val in ar if val < pivot less.push(val) else more.push(val) qsort(less).concat([pivot], qsort(more))

module.exports = qsort

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...compiles to this:

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dean@hdh:~/Devel/coffee$ coffee -cp qsort.coffee // Generated by CoffeeScript 1.4.0(function() { var qsort;

qsort = function(ar) { var less, more, pivot, val, _i, _len; if (!(ar.length > 1)) { return ar; } pivot = ar.pop(); less = []; more = []; for (_i = 0, _len = ar.length; _i < _len; _i++) { val = ar[_i]; if (val < pivot) { less.push(val); } else { more.push(val); } } return qsort(less).concat([pivot], qsort(more)); };

module.exports = qsort;

}).call(this);dean@hdh:~/Devel/coffee$

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2. Program with class

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Wednesday, June 5, 13

(me, 16 months ago)

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There’s only one way to do it.

It reduces mental overhead for devs.

It just works.

Because! With class...

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__extends = function(child, parent) { for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child;};

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__extends = function(child, parent) { for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child;};

Tricksy! And...

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// Generated by CoffeeScript 1.4.0(function() { var Greet, Hello, __hasProp = {}.hasOwnProperty;

Greet = (function() {

function Greet() {}

Greet.prototype.greet = function() { return 'hi'; };

return Greet;

})();

Hello = (function(_super) {

__extends(Hello, _super);

function Hello() { return Hello.__super__.constructor.apply(this, arguments); }

Hello.prototype.hello = function() { return 'hello'; };

return Hello;

})(Greet);

}).call(this);

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// Generated by CoffeeScript 1.4.0(function() { var Greet, Hello, __hasProp = {}.hasOwnProperty;

Greet = (function() {

function Greet() {}

Greet.prototype.greet = function() { return 'hi'; };

return Greet;

})();

Hello = (function(_super) {

__extends(Hello, _super);

function Hello() { return Hello.__super__.constructor.apply(this, arguments); }

Hello.prototype.hello = function() { return 'hello'; };

return Hello;

})(Greet);

}).call(this); ...verbose

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vs.

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class Greet greet: -> 'hi'

class Hello extends Greet hello: -> 'hello'

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3. Use comprehension

idioms!!!!!

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# what's wrong with this code?_ = require 'underscore'

ar = [1,2,3,4,5,6,7,8,9]

doubled = _.map(ar, (x) -> x * 2)

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doubled = i * 2 for i in ar

YOU DON’T NEEDA LIBRARY!!!

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// Generated by CoffeeScript 1.4.0(function() { var ar, i, map, _i, _len;

ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

for (_i = 0, _len = ar.length; _i < _len; _i++) { i = ar[_i]; map = i * 2; }

}).call(this);

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// Generated by CoffeeScript 1.4.0(function() { var ar, i, map, _i, _len;

ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

for (_i = 0, _len = ar.length; _i < _len; _i++) { i = ar[_i]; map = i * 2; }

}).call(this);

This is also faster.

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ar = [1,2,3,4,5,6,7,8,9,10]

aSelect = i for i in ar when (i % 2) == 0aMap = i * 2 for i in araFind = (i for i in ar when i == 0)[0]

Similarly...

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4. One class per file

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Node.js provides a synchronous require

Stitch and browserify use node semantics

Require.js does AMD

How? A library.

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5. Watch your return values.

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dontRunInATightLoop = (object) -> # I meant to mutate this object and return void... object[k] = "#{v}-derp" for k, v of object

This...

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dontRunInATightLoop = function(object) { var k, v, _results; _results = []; for (k in object) { v = object[k]; _results.push(object[k] = "" + v + "-derp"); } return _results;};

...compiles to this.

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Comprehensions+

Implicit returns

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=many allocations

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okayToRunInATightLoop = (object) -> object[k] = "#{v}-derp" for k, v of object # I need to do it explicitly return

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Questions?

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Thanks!@deanero

http://ranch.ero.com(I’m hiring Rubyists!)

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