StackPush.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){
        //create new node
        let node = new Node(value)
        
        // check if the first node is valid
        if(!this.first){
          
         //if not, make the new node the first and last node of the stack
          this.first = node
          this.last = node
        }else{
         // if there is at least one node in the stack
         // make new node to be the first and the previous 
         // first node to be the next property of the new first 
           let temp = this.first
           this.first = node
           this.first.next = temp
        }
      
       // increment the size
       this.size++
      
      return this.size
    }
  
}