add Generating a Unique ID recipe

Author: phlipper

chapters/strings/generating-a-unique-id.md

@@ -0,0 +1,28 @@
+---
+layout: recipe
+title: Generating a Unique ID
+chapter: Strings
+---
+## Problem
+
+You want to generate a random unique identifier.
+
+## Solution
+
+You can create a Base 36 encoded string from a random number.
+
+{% highlight coffeescript %}
+uniqueId = (length=8) ->
+  id = ""
+  id += Math.random().toString(36).substr(2) while id.length < length
+  id.substr 0, length
+
+uniqueId()    # => n5yjla3b
+uniqueId(2)   # => 0d
+uniqueId(20)  # => ox9eo7rt3ej0pb9kqlke
+uniqueId(40)  # => xu2vo4xjn4g0t3xr74zmndshrqlivn291d584alj
+{% endhighlight %}
+
+## Discussion
+
+There are other possible techniques, but this is relatively performant and flexible.