Add insert function to array.builders

Author: Alejandro Carrau

test/array.builders.js

@@ -208,4 +208,9 @@ $(document).ready(function() {
     deepEqual(_.combinations(["a",["b"]],[[1]]),[["a",[1]],[["b"],[1]]],'initial arrays can contain array elements which are then preserved');
   });
 
+  test('insert', function(){
+    deepEqual(_.insert([], 0, 1), [1],'empty array will will insert item');
+    deepEqual(_.insert([1,3], 1, 2), [1,2,3],'array will insert item');
+    deepEqual(_.insert([1,3], 2, 2), [1,3,2],'exceeding index will insert item at the end');
+  });
 });

underscore.array.builders.js

@@ -196,6 +196,13 @@
           }));
         },[]);
       },_.map(arguments[0],function(i){return [i];}));
+    },
+    
+    // Inserts an item in an array at the specific index
+    insert: function(array, index, item){
+      var copy = array.slice(0);
+      copy.splice(index, 0, item);
+      return copy;
     }
 
   });