index.js

'use strict';

/**
 * Custom exception related with stack
 * @param {string} message - message which will be shown when exception will be thrown
 */
export function StackException(message) {
  this.message = message;
  this.name = "StackException";
}

/** Class representing a stack data structure. */
export class Stack {

  /**
   * Initialize stack as empty.
   */
  constructor(...elements) {
    this._stack = [];
    this._stack.push(...elements);
    this._lastIndex = elements.length > 0
      ? elements.length - 1
      : 0;
  }

  /**
   * Puts element into stack.
   * @param {object} elem - object which will be putted into stack
   * @return {Stack} stack with pushed element.
   */
  push(elem) {
    if (elem === undefined) {
      throw new StackException("Parameter should not be empty");
    }
    if (this._stack.length === 0) {
      this._stack[0] = elem;
    }
    else {
      this._lastIndex++;
      this._stack[this._lastIndex] = elem;
    }

    return this;
  }

  /**
   * Takes top element from the stack. Throws an ```StackException``` when the stack is empty.
   * @return {object} elem which will be taken from stack.
   */
  pop() {
    if (this._stack.length === 0) {
      throw new StackException("Stack is empty");
    }

    let elem = this._stack[this._lastIndex];
    this._stack.splice(this._lastIndex, 1);
    this._lastIndex > 0
      ? this._lastIndex--
      : 0;
    return elem;
  }

  /**
   * Peeks at the top element of the stack. Throws an ```Error``` when the stack is empty.
   * @return {object} elem - object which will be picked from stack.
   */
  peek() {
    if (this._stack.length === 0) {
      throw new StackException("Stack is empty");
    }

    return this._stack[this._lastIndex];
  }

  /**
   * Returns the size of the stack. 
   * @return {number} size of stack.
   */
  get size() {
    return this._stack.length;
  }
}