diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/add-a-new-element-to-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/add-a-new-element-to-a-binary-search-tree.english.md
index 82cb596635..cafec3f7de 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/add-a-new-element-to-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/add-a-new-element-to-a-binary-search-tree.english.md
@@ -64,50 +64,24 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  isBinarySearchTree() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var check = true;
-      function checkTree(node) {
-        if (node.left != null) {
-          var left = node.left;
-          if (left.value > node.value) {
-            check = false;
-          } else {
-            checkTree(left);
-          }
-        }
-        if (node.right != null) {
-          var right = node.right;
-          if (right.value < node.value) {
-            check = false;
-          } else {
-            checkTree(right);
-          }
-        }
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    inOrder() {
+      if (!this.root) {
+        return null;
       }
-      checkTree(this.root);
-      return check;
+      var result = new Array();
+      function traverseInOrder(node) {
+        node.left && traverseInOrder(node.left);
+        result.push(node.value);
+        node.right && traverseInOrder(node.right);
+      }
+      traverseInOrder(this.root);
+      return result;
     }
   }
-};
-BinarySearchTree.prototype = {
-  inOrder() {
-    if (!this.root) {
-      return null;
-    }
-    var result = new Array();
-    function traverseInOrder(node) {
-      node.left && traverseInOrder(node.left);
-      result.push(node.value);
-      node.right && traverseInOrder(node.right);
-    }
-    traverseInOrder(this.root);
-    return result;
-  }
-};
+);
 ```
 
 </div>
@@ -133,7 +107,6 @@ function BinarySearchTree() {
       const searchTree = function(current) {
         if (current.value > element) {
           if (current.left) {
-            //si existe
             return searchTree(current.left);
           } else {
             current.left = new Node(element);
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/check-if-an-element-is-present-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/check-if-an-element-is-present-in-a-binary-search-tree.english.md
index 13315c5f2a..246689953b 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/check-if-an-element-is-present-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/check-if-an-element-is-present-in-a-binary-search-tree.english.md
@@ -61,36 +61,39 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
-      function searchTree(node) {
-        if (value < node.value) {
-          if (node.left == null) {
-            node.left = new Node(value);
-            return;
-          } else if (node.left != null) {
-            return searchTree(node.left);
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        function searchTree(node) {
+          if (value < node.value) {
+            if (node.left == null) {
+              node.left = new Node(value);
+              return;
+            } else if (node.left != null) {
+              return searchTree(node.left);
+            }
+          } else if (value > node.value) {
+            if (node.right == null) {
+              node.right = new Node(value);
+              return;
+            } else if (node.right != null) {
+              return searchTree(node.right);
+            }
+          } else {
+            return null;
           }
-        } else if (value > node.value) {
-          if (node.right == null) {
-            node.right = new Node(value);
-            return;
-          } else if (node.right != null) {
-            return searchTree(node.right);
-          }
-        } else {
-          return null;
         }
+        return searchTree(node);
       }
-      return searchTree(node);
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/create-a-doubly-linked-list.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/create-a-doubly-linked-list.english.md
index 15813dfc2f..c3bc59a6a9 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/create-a-doubly-linked-list.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/create-a-doubly-linked-list.english.md
@@ -68,7 +68,11 @@ var DoublyLinkedList = function() {
 <div id='js-teardown'>
 
 ```js
-DoublyLinkedList.prototype = {
+
+DoublyLinkedList.prototype = Object.assign(
+  DoublyLinkedList.prototype,
+  {
+  
   print() {
     if (this.head == null) {
       return null;
@@ -96,8 +100,8 @@ DoublyLinkedList.prototype = {
       result.push(node.data);
       return result;
     };
-  } 
-};
+  }
+});
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-leaf-node-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-leaf-node-in-a-binary-search-tree.english.md
index 5f1288a3bb..e54507d00d 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-leaf-node-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-leaf-node-in-a-binary-search-tree.english.md
@@ -68,81 +68,57 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
-      function searchTree(node) {
-        if (value < node.value) {
-          if (node.left == null) {
-            node.left = new Node(value);
-            return;
-          } else if (node.left != null) {
-            return searchTree(node.left);
-          }
-        } else if (value > node.value) {
-          if (node.right == null) {
-            node.right = new Node(value);
-            return;
-          } else if (node.right != null) {
-            return searchTree(node.right);
-          }
-        } else {
-          return null;
-        }
-      }
-      return searchTree(node);
-    }
-  },
-  inorder: function() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var result = new Array();
-      function traverseInOrder(node) {
-        if (node.left != null) {
-          traverseInOrder(node.left);
-        }
-        result.push(node.value);
-        if (node.right != null) {
-          traverseInOrder(node.right);
-        }
-      }
-      traverseInOrder(this.root);
-      return result;
-    }
-  },
-  isBinarySearchTree() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var check = true;
-      function checkTree(node) {
-        if (node.left != null) {
-          var left = node.left;
-          if (left.value > node.value) {
-            check = false;
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        function searchTree(node) {
+          if (value < node.value) {
+            if (node.left == null) {
+              node.left = new Node(value);
+              return;
+            } else if (node.left != null) {
+              return searchTree(node.left);
+            }
+          } else if (value > node.value) {
+            if (node.right == null) {
+              node.right = new Node(value);
+              return;
+            } else if (node.right != null) {
+              return searchTree(node.right);
+            }
           } else {
-            checkTree(left);
-          }
-        }
-        if (node.right != null) {
-          var right = node.right;
-          if (right.value < node.value) {
-            check = false;
-          } else {
-            checkTree(right);
+            return null;
           }
         }
+        return searchTree(node);
+      }
+    },
+    inorder: function() {
+      if (this.root == null) {
+        return null;
+      } else {
+        var result = new Array();
+        function traverseInOrder(node) {
+          if (node.left != null) {
+            traverseInOrder(node.left);
+          }
+          result.push(node.value);
+          if (node.right != null) {
+            traverseInOrder(node.right);
+          }
+        }
+        traverseInOrder(this.root);
+        return result;
       }
-      checkTree(this.root);
-      return check;
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-one-child-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-one-child-in-a-binary-search-tree.english.md
index 45fc931b75..1d20c1e688 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-one-child-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-one-child-in-a-binary-search-tree.english.md
@@ -106,81 +106,57 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
-      function searchTree(node) {
-        if (value < node.value) {
-          if (node.left == null) {
-            node.left = new Node(value);
-            return;
-          } else if (node.left != null) {
-            return searchTree(node.left);
-          }
-        } else if (value > node.value) {
-          if (node.right == null) {
-            node.right = new Node(value);
-            return;
-          } else if (node.right != null) {
-            return searchTree(node.right);
-          }
-        } else {
-          return null;
-        }
-      }
-      return searchTree(node);
-    }
-  },
-  inorder: function() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var result = new Array();
-      function traverseInOrder(node) {
-        if (node.left != null) {
-          traverseInOrder(node.left);
-        }
-        result.push(node.value);
-        if (node.right != null) {
-          traverseInOrder(node.right);
-        }
-      }
-      traverseInOrder(this.root);
-      return result;
-    }
-  },
-  isBinarySearchTree() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var check = true;
-      function checkTree(node) {
-        if (node.left != null) {
-          var left = node.left;
-          if (left.value > node.value) {
-            check = false;
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        function searchTree(node) {
+          if (value < node.value) {
+            if (node.left == null) {
+              node.left = new Node(value);
+              return;
+            } else if (node.left != null) {
+              return searchTree(node.left);
+            }
+          } else if (value > node.value) {
+            if (node.right == null) {
+              node.right = new Node(value);
+              return;
+            } else if (node.right != null) {
+              return searchTree(node.right);
+            }
           } else {
-            checkTree(left);
-          }
-        }
-        if (node.right != null) {
-          var right = node.right;
-          if (right.value < node.value) {
-            check = false;
-          } else {
-            checkTree(right);
+            return null;
           }
         }
+        return searchTree(node);
+      }
+    },
+    inorder: function() {
+      if (this.root == null) {
+        return null;
+      } else {
+        var result = new Array();
+        function traverseInOrder(node) {
+          if (node.left != null) {
+            traverseInOrder(node.left);
+          }
+          result.push(node.value);
+          if (node.right != null) {
+            traverseInOrder(node.right);
+          }
+        }
+        traverseInOrder(this.root);
+        return result;
       }
-      checkTree(this.root);
-      return check;
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-two-children-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-two-children-in-a-binary-search-tree.english.md
index cd6bd7ea81..a7e48c8dc4 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-two-children-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/delete-a-node-with-two-children-in-a-binary-search-tree.english.md
@@ -125,81 +125,84 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
-      function searchTree(node) {
-        if (value < node.value) {
-          if (node.left == null) {
-            node.left = new Node(value);
-            return;
-          } else if (node.left != null) {
-            return searchTree(node.left);
-          }
-        } else if (value > node.value) {
-          if (node.right == null) {
-            node.right = new Node(value);
-            return;
-          } else if (node.right != null) {
-            return searchTree(node.right);
-          }
-        } else {
-          return null;
-        }
-      }
-      return searchTree(node);
-    }
-  },
-  inorder: function() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var result = new Array();
-      function traverseInOrder(node) {
-        if (node.left != null) {
-          traverseInOrder(node.left);
-        }
-        result.push(node.value);
-        if (node.right != null) {
-          traverseInOrder(node.right);
-        }
-      }
-      traverseInOrder(this.root);
-      return result;
-    }
-  },
-  isBinarySearchTree() {
-    if (this.root == null) {
-      return null;
-    } else {
-      var check = true;
-      function checkTree(node) {
-        if (node.left != null) {
-          var left = node.left;
-          if (left.value > node.value) {
-            check = false;
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        function searchTree(node) {
+          if (value < node.value) {
+            if (node.left == null) {
+              node.left = new Node(value);
+              return;
+            } else if (node.left != null) {
+              return searchTree(node.left);
+            }
+          } else if (value > node.value) {
+            if (node.right == null) {
+              node.right = new Node(value);
+              return;
+            } else if (node.right != null) {
+              return searchTree(node.right);
+            }
           } else {
-            checkTree(left);
-          }
-        }
-        if (node.right != null) {
-          var right = node.right;
-          if (right.value < node.value) {
-            check = false;
-          } else {
-            checkTree(right);
+            return null;
           }
         }
+        return searchTree(node);
+      }
+    },
+    inorder: function() {
+      if (this.root == null) {
+        return null;
+      } else {
+        var result = new Array();
+        function traverseInOrder(node) {
+          if (node.left != null) {
+            traverseInOrder(node.left);
+          }
+          result.push(node.value);
+          if (node.right != null) {
+            traverseInOrder(node.right);
+          }
+        }
+        traverseInOrder(this.root);
+        return result;
+      }
+    },
+    isBinarySearchTree() {
+      if (this.root == null) {
+        return null;
+      } else {
+        var check = true;
+        function checkTree(node) {
+          if (node.left != null) {
+            var left = node.left;
+            if (left.value > node.value) {
+              check = false;
+            } else {
+              checkTree(left);
+            }
+          }
+          if (node.right != null) {
+            var right = node.right;
+            if (right.value < node.value) {
+              check = false;
+            } else {
+              checkTree(right);
+            }
+          }
+        }
+        checkTree(this.root);
+        return check;
       }
-      checkTree(this.root);
-      return check;
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-height-of-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-height-of-a-binary-search-tree.english.md
index dfe2d6244a..41021e359c 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-height-of-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-height-of-a-binary-search-tree.english.md
@@ -66,13 +66,10 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
       function searchTree(node) {
         if (value < node.value) {
           if (node.left == null) {
@@ -92,10 +89,17 @@ BinarySearchTree.prototype = {
           return null;
         }
       }
-      return searchTree(node);
+
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        return searchTree(node);
+      }
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-value-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-value-in-a-binary-search-tree.english.md
index e2cb2364a4..2141c693e7 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-value-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/find-the-minimum-and-maximum-value-in-a-binary-search-tree.english.md
@@ -61,13 +61,10 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
       function searchTree(node) {
         if (value < node.value) {
           if (node.left == null) {
@@ -87,10 +84,17 @@ BinarySearchTree.prototype = {
           return null;
         }
       }
-      return searchTree(node);
+
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        return searchTree(node);
+      }
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/invert-a-binary-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/invert-a-binary-tree.english.md
index 9d3d8f1d30..318f55e2ea 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/invert-a-binary-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/invert-a-binary-tree.english.md
@@ -58,54 +58,58 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
     add: function(value) {
-        var node = this.root;
-        if (node == null) {
-          this.root = new Node(value);
-          return;
+      function searchTree(node) {
+        if (value < node.value) {
+          if (node.left == null) {
+            node.left = new Node(value);
+            return;
+          } else if (node.left != null) {
+            return searchTree(node.left)
+          };
+        } else if (value > node.value) {
+          if (node.right == null) {
+            node.right = new Node(value);
+            return;
+          } else if (node.right != null) {
+            return searchTree(node.right);
+          };
         } else {
-            function searchTree(node) {
-                if (value < node.value) {
-                    if (node.left == null) {
-                        node.left = new Node(value);
-                        return;
-                    } else if (node.left != null) {
-                        return searchTree(node.left)
-                    };
-                } else if (value > node.value) {
-                    if (node.right == null) {
-                        node.right = new Node(value);
-                        return;
-                    } else if (node.right != null) {
-                        return searchTree(node.right);
-                    };
-                } else {
-                    return null;
-                };
-            };
-            return searchTree(node);
+          return null;
         };
+      }
+
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        return searchTree(node);
+      };
     },
     inorder: function() {
-        if (this.root == null) {
-          return null;
-        } else {
-          var result = new Array();
-          function traverseInOrder(node) {
-              if (node.left != null) {
-                  traverseInOrder(node.left);
-              };
-              result.push(node.value);
-              if (node.right != null) {
-                  traverseInOrder(node.right);
-              };
-          }
-          traverseInOrder(this.root);
-          return result;
-        };
+      if (this.root == null) {
+        return null;
+      } else {
+        var result = new Array();
+        function traverseInOrder(node) {
+          if (node.left != null) {
+            traverseInOrder(node.left);
+          };
+          result.push(node.value);
+          if (node.right != null) {
+            traverseInOrder(node.right);
+          };
+        }
+        traverseInOrder(this.root);
+        return result;
+      };
     }
-};
+  }
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/reverse-a-doubly-linked-list.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/reverse-a-doubly-linked-list.english.md
index c634f9fe67..08a4650c9e 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/reverse-a-doubly-linked-list.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/reverse-a-doubly-linked-list.english.md
@@ -63,52 +63,55 @@ var DoublyLinkedList = function() {
 <div id='js-teardown'>
 
 ```js
-DoublyLinkedList.prototype = {
-  add(data) {
-    if (this.head == null) {
-      this.head = new Node(data, null);
-      this.tail = this.head;
-    } else {
-      var node = this.head;
-      var prev = null;
-      while (node.next != null) {
-        prev = node;
-        node = node.next;
+DoublyLinkedList.prototype = Object.assign(
+  DoublyLinkedList.prototype,
+  {
+    add(data) {
+      if (this.head == null) {
+        this.head = new Node(data, null);
+        this.tail = this.head;
+      } else {
+        var node = this.head;
+        var prev = null;
+        while (node.next != null) {
+          prev = node;
+          node = node.next;
+        };
+        var newNode = new Node(data, node);
+        node.next = newNode;
+        this.tail = newNode;
       };
-      var newNode = new Node(data, node);
-      node.next = newNode;
-      this.tail = newNode;
-    };
-  },
-  print() {
-    if (this.head == null) {
-      return null;
-    } else {
-      var result = new Array();
-      var node = this.head;
-      while (node.next != null) {
+    },
+    print() {
+      if (this.head == null) {
+        return null;
+      } else {
+        var result = new Array();
+        var node = this.head;
+        while (node.next != null) {
+          result.push(node.data);
+          node = node.next;
+        };
         result.push(node.data);
-        node = node.next;
+        return result;
       };
-      result.push(node.data);
-      return result;
-    };
-  },
-  printReverse() {
-    if (this.tail == null) {
-      return null;
-    } else {
-      var result = new Array();
-      var node = this.tail;
-      while (node.prev != null) {
+    },
+    printReverse() {
+      if (this.tail == null) {
+        return null;
+      } else {
+        var result = new Array();
+        var node = this.tail;
+        while (node.prev != null) {
+          result.push(node.data);
+          node = node.prev;
+        };
         result.push(node.data);
-        node = node.prev;
+        return result;
       };
-      result.push(node.data);
-      return result;
-    };
+    }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-breadth-first-search-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-breadth-first-search-in-a-binary-search-tree.english.md
index e15df85f49..2c5bbc1bef 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-breadth-first-search-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-breadth-first-search-in-a-binary-search-tree.english.md
@@ -64,13 +64,10 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
       function searchTree(node) {
         if (value < node.value) {
           if (node.left == null) {
@@ -90,10 +87,16 @@ BinarySearchTree.prototype = {
           return null;
         }
       }
-      return searchTree(node);
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        return searchTree(node);
+      }
     }
   }
-};
+);
 ```
 
 </div>
diff --git a/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-depth-first-search-in-a-binary-search-tree.english.md b/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-depth-first-search-in-a-binary-search-tree.english.md
index bb35aadb2a..914799aab3 100644
--- a/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-depth-first-search-in-a-binary-search-tree.english.md
+++ b/curriculum/challenges/english/08-coding-interview-prep/data-structures/use-depth-first-search-in-a-binary-search-tree.english.md
@@ -76,13 +76,10 @@ function BinarySearchTree() {
 <div id='js-teardown'>
 
 ```js
-BinarySearchTree.prototype = {
-  add: function(value) {
-    var node = this.root;
-    if (node == null) {
-      this.root = new Node(value);
-      return;
-    } else {
+BinarySearchTree.prototype = Object.assign(
+  BinarySearchTree.prototype,
+  {
+    add: function(value) {
       function searchTree(node) {
         if (value < node.value) {
           if (node.left == null) {
@@ -102,10 +99,18 @@ BinarySearchTree.prototype = {
           return null;
         }
       }
-      return searchTree(node);
+
+      var node = this.root;
+      if (node == null) {
+        this.root = new Node(value);
+        return;
+      } else {
+        return searchTree(node);
+      }
     }
   }
-};
+);
+
 ```
 
 </div>