Data Structure in JavaScript

linkedList.js

// Linked List implementation
class Node {
  constructor(data, next = null) {
    this.data = data;
    this.next = next;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
    this.size = 0;
  }
  
  // Insert first node
  insertFirst(data) {
    this.head = new Node(data, this.head)
    this.size++;
  }
  // Insert last node
  insertLast(data) {
    const node = new Node(data)
    let current;
    
    // if empty make the head
    if (!this.head) {
      this.head = node;
    } else {
      current = this.head;
      while(current.next) {
        current = current.next;
      }
      current.next = node;
    }
    this.size++;
  }
  // Insert at index
  insertAt(data, index) {
    // if index is out of reange do nothing
    if(index > 0 && index > this.size) {
      return;
    }
    
    // if first index
    if (index === 0) {
      this.insertFirst(data);
      return;
    }
    
    const node = new Node(data);
    let current;
    let previous;
    
    current = this.head;
    let count = 0;
    while(count < index) {
      previous = current // node before index
      count++;
      current = current.next; // node after index
    }
    
    node.next = current;
    previous.next = node;
    
    this.size++;
  }
  // Get at index
  getAt(index) {
    let current = this.head;
    let count = 0;
    while(current) {
      if (count === index) {
        console.log(current.data);
      }
      count++;
      current = current.next;
    }
    
    return null;
  }
  // Remove at index
  removeAt(index) {
    if (index > 0 && index > this.size) {
      return;
    }
    
    let current = this.head;
    let count = 0;
    let previous;
    
    // remove first
    if (index === 0 ) {
      this.head = current.next;
    } else {
      while(count < index) {
        count++;
        previous = current;
        current = current.next;
      }
      
      previous.next = current.next;
    }
    this.size--;
  }
  // Clear list
  clear() {
    this.head = null;
    this.size = 0;
  }
  // Print list
  printListData() {
    let current = this.head;
    while(current) {
      console.log(current.data);
      current = current.next;
    }
  }
  
}

const ll = new LinkedList();
ll.insertFirst(100);
ll.insertFirst(200);
ll.insertFirst(300);
ll.insertLast(50);
ll.insertAt(500, 2)
ll.removeAt(2)
ll.clear();
ll.insertFirst(100);

ll.printListData();

queue.js

class Queue {
  constructor() {
    this.items = {};
    this.count = 0;
    this.head = 0;
  }
  
  // add item
  enqueue(item) {
    this.items[this.count] = item;
    this.count++;
  } 
  
  // remove first element 
  dequeue() {
    const item = this.items[this.head];
    delete this.items[this.head];
    this.head++;
    return item;
  }
  
  peek() {
    return this.items[this.head]
  }
  
  getSize() {
    return this.count - this.head;
  }
  
  isEmpty() {
    return this.getSize() === 0;
  }
}

const queue = new Queue();
queue.enqueue({ id: 1, value: 100 });
queue.enqueue({ id: 2, value: 200 });
queue.enqueue({ id: 3, value: 300 });

console.log("size: ", queue.getSize());
queue.dequeue();
console.log("size: ", queue.getSize());
console.log("head: ", queue.peek());
console.log("isEmpty ", queue.isEmpty());
queue.dequeue();
queue.dequeue();
console.log("isEmpty ", queue.isEmpty());
console.log(queue.items);

stack.js

class Stack {
  constructor() {
    this.items = [];
    this.count = 0;
  }
  
  push(element) {
    this.items[this.count] = element;
    console.log("Item " + element + " added to " + this.count);
    this.count += 1;
    
    return this.count - 1;
  }
  
  pop() {
    if (this.count === 0) return undefined;
    const deletedItem = this.items[this.count -1];
    this.count -= 1;
    
    console.log("Item deleted:" + deletedItem);
    
    return deletedItem;
  }
  
  peek() {
    console.log("Top element " + this.items[this.count -1])
    return this.items[this.count - 1];
  }
  
  isEmpty() {
    return this.count === 0;
  }
  
  size() {
    return this.count;
  }
  
  print() {
    let str = "";
    for (let i=0; i < this.count; i++) {
      str += this.items[i] + " ";
    }
    console.log("stack items: ", str);
    return str;
  }
  
  clear() {
    this.items = [];
    this.count = 0;
    console.log("Stack cleared")
  }
}

const stack = new Stack();

stack.push(100);
stack.push(200);
stack.push(300);

stack.print();

stack.pop();

stack.peek();
console.log("is empty? ", stack.isEmpty())
stack.print();
stack.pop();
stack.clear();
stack.print();
stack.pop();
stack.peek();
console.log("is empty? ", stack.isEmpty())