Add insertion-sort and associated test

solutions/javascript/insertion-sort.js

@@ -0,0 +1,44 @@
+// insertion-sort
+'use strict';
+
+module.exports = function (array, compare) {
+  // Not an array, empty or array of 1 is already sorted
+  if (!Array.isArray(array) || array.length < 2) {
+    return array;
+  }
+
+  // Swap elements of the array
+  var swap = function (array, first, second) {
+    var temp = array[first];
+    array[first] = array[second];
+    array[second] = temp;
+    return array;
+  };
+
+  // Create a compare function if one is not passed in
+  if (typeof compare !== 'function') {
+    compare = function (a, b) {
+      return a > b ? 1 : -1;
+    };
+  }
+
+  var i, j;
+
+  /*
+   * Assume first element is sorted
+   * Add first unsorted element to sorted array
+   * Compare new element in sorted array with previous elements
+   *   to determine correct destination index in sorted array
+   */
+
+  for (i = 1; i < array.length; i++) {
+    j = i;
+    // Make sure we don't walk off the array and compare until sorted
+    while ((j - 1) >= 0 && compare(array[j], array[j - 1]) < 0) {
+      swap(array, j, j-1);
+      j--;
+    }
+  }
+
+  return array;
+};

tests/javascript/insertion-sort.js

@@ -0,0 +1,13 @@
+var assert = require('assert');
+var insertion = require('../../solutions/javascript/insertion-sort');
+
+describe('sort functions ->', function(){
+    var sorted = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    var array = [9, 8, 7, 6, 5, 4, 3, 2, 1];
+
+    it("sort array: " + sorted, function(){
+      array = insertion(array);
+      assert.deepEqual(array, sorted);
+    })
+})
+