add recipe for lowercasing a string

Author: phlipper

chapters/strings/lowercasing-a-string.md

@@ -0,0 +1,45 @@
+---
+layout: recipe
+title: Lowercasing a String
+chapter: Strings
+---
+## Problem
+
+You want to lowercase a string.
+
+## Solution
+
+Use JavaScript's String toLowerCase() method:
+
+{% highlight coffeescript %}
+"ONE TWO THREE".toLowerCase()
+# => 'one two three'
+{% endhighlight %}
+
+## Discussion
+
+`toLowerCase()` is a standard JavaScript method. Don't forget the parentheses.
+
+### Syntax Sugar
+
+You can add some Ruby-like syntax sugar with the following shortcut:
+
+{% highlight coffeescript %}
+String::downcase = -> @toLowerCase()
+"ONE TWO THREE".downcase()
+# => 'one two three'
+{% endhighlight %}
+
+The snippet above demonstrates a few features of CoffeeScript:
+
+* The double-colon `::` is shorthand for saying `.prototype.`
+* The "at" sign `@` is shorthand for saying `this.`
+
+The code above compiles in to the following JavaScript:
+
+{% highlight javascript %}
+String.prototype.downcase = function() {
+  return this.toLowerCase();
+};
+"ONE TWO THREE".downcase();
+{% endhighlight %}