DEVFLAKES

Aug 30

insights of coffee script’s IN and OF loops

We make heavy use of coffee script and usually it can keep its promise to make our coding live a little bit easier. Usually … We knew both the “in” and “of” loop but we never thought about the underlying implementation and the impact IE could have. So I’ll share our two main WTFs so you won’t have to repeat them:

Let’s first have a look how “in” and “of” compiles into JS:

for key, value of arr
  alert key
  alert value

in JS it looks like this:

var key, value, _len; for (key in arr) {
value = arr[key];
alert(key);
alert(value);
}

So “of” becomes” “in” …

for value, key in arr
  alert key
  alert value

—>

for (key = 0, _len = arr.length; key < _len; key++) {
value = arr[key];
alert(key);
alert(value);
}

Do you see the difference? The order of “value” and “key” (key,value vs. value,key) is inverted! WTF?!?! This WILL produce bugs!

The next thing is: You should never use for-in loop on arrays but especially in IE you’ll get into trouble ( http://stackoverflow.com/questions/500504/javascript-for-in-with-arrays ). Hard if you don’t know what will happen behind your coffee script…

So always keep in mind what coffee scripts IN and OF means, that will reduce you WTFs/min

Jul 20

Artflakes Dev-Team on Tumblr

Here the developer team of ARTFLAKES will publish learnings from our daily fight with Ruby on Rails, Node.js, Javascript, MySql, Sphinx and other technologies we love.

Additionally we’ll post release notes about new features on ARTFLAKES.

Feel free to follow us on twitter as well: @devflakes