Data Structures: Add Elements at a Specific Index in a Linked List

Data Structures/linkedListClassAddAtIndex.js

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+// https://www.freecodecamp.org/learn/coding-interview-prep/data-structures/add-elements-at-a-specific-index-in-a-linked-list
+
+function LinkedList() {
+  var length = 0;
+  var head = null;
+
+  var Node = function (element) {
+    this.element = element;
+    this.next = null;
+  };
+
+  this.size = function () {
+    return length;
+  };
+
+  this.head = function () {
+    return head;
+  };
+
+  this.add = function (element) {
+    var node = new Node(element);
+    if (head === null) {
+      head = node;
+    } else {
+      var currentNode = head;
+
+      while (currentNode.next) {
+        currentNode = currentNode.next;
+      }
+
+      currentNode.next = node;
+    }
+    length++;
+  };
+
+  // Only change code below this line
+  this.addAt = (index, element) => {
+    if (index < 0 || index > length) {
+      return false;
+    }
+    let i = 0;
+    let previousNode = null;
+    let nextNode = head;
+    while (i < index && nextNode !== null) {
+      i++;
+      previousNode = nextNode;
+      nextNode = nextNode.next;
+    }
+    if (i != index) {
+      return false;
+    }
+    const node = new Node(element);
+    if (previousNode === null) {
+      head = node;
+    } else {
+      previousNode.next = node;
+    }
+    node.next = nextNode;
+    length++;
+    return true;
+  };
+  // Only change code above this line
+}