Stacks.js

class Node {
    constructor(value){
        this.value = value
        this.next = null
    }

}


class Stack {
    constructor(){
        this.first = null
        this.last = null
        this.size = 0
    
    }

    push(value){
        let node = new Node(value)
        
        if(!this.first){
          this.first = node
          this.last = node
        }else{
           let temp = this.first
           this.first = node
           this.first.next = temp
        }
       this.size++
      
      return this.size
    }
  
  
  pop(){
  
    if(!this.first) return null
    let temp = this.first
    if(this.first === this.last){
          this.last = null
    }
    
    this.first = this.first.next
    this.size--
    return temp.value
  
  
  
  
  }
}