5 things I learned about coffeescript in my year with it

5 things I learned
about coffeescript
(in my year with it)
Wednesday, June 5, 13

Dean Hudson, @deanero
Senior Engineer, Super Secret Music Start Up
(and hiring!)
Who Am I?

1. coffee -cp

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
[...]

to see that this...

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

...compiles to this:

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$

2. Program with
class

(me, 16 months ago)

There’s only one way to do it.
It reduces mental overhead for devs.
It just works.
Because! With
class...

__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;
};

__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...

class Greet
greet: -> 'hi'
class Hello extends Greet
hello: -> 'hello'

3. Use
comprehension
idioms!!!!!

# what's wrong with this code?
_ = require 'underscore'
ar = [1,2,3,4,5,6,7,8,9]
doubled = _.map(ar, (x) -> x * 2)

doubled = i * 2 for i in ar
YOU DON’T NEED
A LIBRARY!!!

(function() {
var ar, i, map, _i, _len;
ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
i = ar[_i];
map = i * 2;
}
}).call(this);

(function() {
var ar, i, map, _i, _len;
ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
i = ar[_i];
map = i * 2;
}
}).call(this);
This is also faster.

ar = [1,2,3,4,5,6,7,8,9,10]
aSelect = i for i in ar when (i % 2) == 0
aMap = i * 2 for i in ar
aFind = (i for i in ar when i == 0)[0]
Similarly...

4. One class per file

Node.js provides a synchronous require
Stitch and browserify use node semantics
Require.js does AMD
How? A library.

5. Watch your
return values.

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

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.

Comprehensions
+
Implicit returns

=
many allocations

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

Questions?

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

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