added recipe for checking type of value is array

chapters/arrays/check-type-is-array.md

@@ -0,0 +1,44 @@
+---
+layout: recipe
+title: Check if type of value is an Array
+chapter: Arrays
+---
+## Problem
+
+You want to check if a value is an `Array`.
+
+{% highlight coffeescript %}
+myArray = []
+console.log typeof myArray // outputs 'object'
+{% endhighlight %}
+
+The `typeof` operator gives a faulty output for arrays.
+
+## Solution
+
+Use the following code:
+
+{% highlight coffeescript %}
+typeIsArray = Array.isArray || ( value ) -> return {}.toString.call( value ) is '[object Array]'
+{% endhighlight %}
+
+To use this, just call `typeIsArray` as such:
+
+{% highlight coffeescript %}
+myArray = []
+typeIsArray myArray // outputs true
+{% endhighlight %}
+
+## Discussion
+
+The method above has been adopted from "the Miller Device". An alternative is to use Douglas Crockford's snippet:
+
+{% highlight coffeescript %}
+typeIsArray = ( value ) ->
+    value and
+        typeof value is 'object' and
+        value instanceof Array and
+        typeof value.length is 'number' and
+        typeof value.splice is 'function' and
+        not ( value.propertyIsEnumerable 'length' )
+{% endhighlight %}