add Array::push.apply examples to Concatenating Arrays recipe

Author: phlipper

chapters/arrays/concatenating-arrays.md

@@ -9,17 +9,43 @@ You want to join two arrays together.
 
 ## Solution
 
-Use JavaScript's Array concat() method:
+There are two standard options for concatenating arrays in JavaScript.
+
+The first is to use JavaScript's Array `concat()` method:
 
 {% highlight coffeescript %}
-ray1 = [1,2,3]
-ray2 = [4,5,6]
-ray3 = ray1.concat ray2
+array1 = [1, 2, 3]
+array2 = [4, 5, 6]
+array3 = array1.concat array2
 # => [1, 2, 3, 4, 5, 6]
 {% endhighlight %}
 
-## Discussion
+Note that `array1` is _not_ modified by the operation. The concatenated array is returned as a new object.
+
+If you want to merge two arrays without creating a new object, you can use the following technique:
+
+{% highlight coffeescript %}
+array1 = [1, 2, 3]
+array2 = [4, 5, 6]
+Array::push.apply array1, array2
+array1
+# => [1, 2, 3, 4, 5, 6]
+{% endhighlight %}
+
+In the example above, the `Array.prototype.push.apply(a, b)` approach modifies `array1` in place without creating a new array object.
 
-CoffeeScript lacks a special syntax for joining arrays, but concat is a standard JavaScript method.
+We can simplify the pattern above using CoffeeScript by creating a new `merge()` method for Arrays.
+
+{% highlight coffeescript %}
+Array::merge = (other) -> Array::push.apply @, other
+
+array1 = [1, 2, 3]
+array2 = [4, 5, 6]
+array1.merge array2
+array1
+# => [1, 2, 3, 4, 5, 6]
+{% endhighlight %}
+
+## Discussion
 
-Note that ray1 is _not_ modified by the operation. The concatenated array is returned as a new object.
+CoffeeScript lacks a special syntax for joining arrays, but `concat()` and `push()` are standard JavaScript methods.