Creating a queue

Of the four types of the queue that we have discussed earlier, first, we will implement a simple queue and then move on to modify it for each type of the subsequent queue.

A simple queue

Similar to a stack, we will create a queue using the following steps:

1. Define aconstructor():

class Queue {
    constructor() {

    }
}

2. We will be using WeakMap() for in-memory data storage just like we did for stacks: 

    const qKey = {};
    const items = new WeakMap();

    class Queue {
        constructor() {

        }
    }

3. Implement the methods described previously in the API:

var Queue = (() => {
    const qKey = {};
    const items = new WeakMap();

    class Queue {

        constructor() {
            items.set(qKey, []);
        }

        add(element) {
            let queue = items.get(qKey);
            queue.push(element);
        }

        remove() {
            let queue = items.get(qKey);
            return queue.shift();
        }

        peek() {
            let queue...