Answers for "data structures and algorithms using javascript es6 and beyong pdf"

startsWith() and endsWith() functions in PHP

function startsWith($haystack, $needle)
{
     $length = strlen($needle);
     return (substr($haystack, 0, $length) === $needle);
}

function endsWith($haystack, $needle)
{
    $length = strlen($needle);
    if ($length == 0) {
        return true;
    }

    return (substr($haystack, -$length) === $needle);
}

queue data structure in javascript 2018

var Queue = (()=>{
  const map = new WeakMap();
  let _items = []
  class Queue{
    constructor(...items){
      //initialize the items in queue
      map.set(this, []);
      _items = map.get(this);
      // enqueuing the items passed to the constructor
      this.enqueue(...items)
    }
    
    enqueue(...items){
      //push items into the queue
      this._items = [...this._items, ...items]
      return this._items;
    }
    
    dequeue(count=1){
      //pull out the first item from the queue
      _items.splice(0,count);
      return this._items;
    }
    
    peek(){
      //peek at the first item from the queue
      return _items[0]
    }
    
    size(){
      //get the length of queue
      return _items.length
    }
    
    isEmpty(){
      //find whether the queue is empty or no
      return _items.length===0
    }
    
    toArray(){
      return _items
    }
    
  }
  return Queue
})()