232. Implement Queue using Stacks.js

/**
 * Initialize your data structure here.
 */
var MyQueue = function () {
    this.pushStack = new Stack()
    this.popStack = new Stack()
};

/**
 * Push element x to the back of queue. 
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function (x) {
    this.pushStack.push(x)
};

/**
 * Removes the element from in front of queue and returns that element.
 * @return {number}
 */
MyQueue.prototype.pop = function () {
    if (this.popStack.empty()) {
        while (!this.pushStack.empty()) {
            this.popStack.push(this.pushStack.pop())
        }
    }
    return this.popStack.pop()
};

/**    
 * Get the front element.
 * @return {number} 
 */
MyQueue.prototype.peek = function () {
    if (this.popStack.empty()) {
        while (!this.pushStack.empty()) {
            this.popStack.push(this.pushStack.pop())

        }
    }
    return this.popStack.peek()
};

/**
 * Returns whether the queue is empty.
 * @return {boolean}
 */
MyQueue.prototype.empty = function () {
    return this.popStack.empty() && this.pushStack.empty()
};

/** 
 * Your MyQueue object will be instantiated and called as such:
 * var obj = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */

class Stack {
    constructor() {
        this.storage = {};
        this.size = 0;
    }

    push(val) {
        this.storage[this.size] = val;
        this.size++;
    }

    pop() {
        let top = this.storage[this.size - 1];
        this.size--;
        delete this.storage[this.size];
        return top;
    }

    peek() {
        return this.storage[this.size - 1];
    }

    empty() {
        return this.size === 0;
    }

    getSize() {
        return this.size;
    }
}