stack.js

/* Stack data-structure. It's work is based on the LIFO method (last-IN-first-OUT).
 * It means that elements added to the stack are placed on the top and only the
 * last element (from the top) can be reached. After we get access to the last
 * element, he pops from the stack.
 * This is a class-based implementation of a Stack. It provides functions
 * 'push' - to add an element, 'pop' - to remove an element from the top.
 * Also it implements 'length', 'last' and 'isEmpty' properties and
 * static isStack method to check is an object the instance of Stack class.
 */

// Class declaration
class Stack {
  constructor() {
    this.stack = []
    this.top = 0
  }

  // Adds a value to the end of the Stack
  push( newValue ) {
    this.stack.push( newValue )
    this.top += 1
  }

  // Returns and removes the last element of the Stack
  pop() {
    if ( this.top !== 0 ) {
      this.top -= 1
      return this.stack.pop()
    }
    throw new Error( 'Stack Underflow' )
  }

  // Returns the number of elements in the Stack
  get length() {
    return this.top
  }

  // Returns true if stack is empty, false otherwise
  get isEmpty() {
    return this.top === 0
  }

  // Returns the last element without removing it
  get last() {
    if ( this.top !== 0 ) {
      return this.stack[ this.stack.length - 1 ]
    }
    return null
  }

  // Checks if an object is the instance os the Stack class
  static isStack( el ) {
    return el instanceof Stack
  }
}
const newStack = new Stack()
console.log( 'Is it a Stack?,', Stack.isStack( newStack ) )
console.log( 'Is stack empty? ', newStack.isEmpty )
newStack.push( 'Hello world' )
newStack.push( 42 )
newStack.push( {
  a: 6,
  b: 7
} )
console.log( 'The length of stack is ', newStack.length )
console.log( 'Is stack empty? ', newStack.isEmpty )
console.log( 'Give me the last one ', newStack.last )
console.log( 'Pop the latest ', newStack.pop() )
console.log( 'Pop the latest ', newStack.pop() )
console.log( 'Pop the latest ', newStack.pop() )
console.log( 'Is stack empty? ', newStack.isEmpty )
/*
| 19: 26: 04 | bryan @LAPTOP - 9 LGJ3JGS: [ Stack ] Stack_exitstatus: 0 __________________________________________________________o >

  node StackES6.js
Is it a Stack ? , true
Is stack empty ? true
The length of stack is 3
Is stack empty ? false
Give me the last one {
  a: 6,
  b: 7
}
Pop the latest {
  a: 6,
  b: 7
}
Pop the latest 42
Pop the latest Hello world
Is stack empty ? true |
  19 : 26: 10 | bryan @LAPTOP - 9 LGJ3JGS: [ Stack ] Stack_exitstatus: 0 __________________________________________________________o >
*/