(Algorithms in Javascript) CTCI 3.4 - Queue via Stacks: Implement a MyQueue class which implements a queue using two stacks.

ctci-3.4-queue-via-stacks.js

//We create 2 stacks one for enqueue and one for dequeue. 
//Once dequeue stack is empty, we pull all elements from enqueue stack onto dequeue stack;
class MyQueue {
	constructor(capacity){
		this._capacity = capacity || Infinity;
		this._dequeue = [];
		this._enqueue = [];
	}

	enqueue(element){
		if(this._enqueue.length < this._capacity){
			this._enqueue.push(element);
			return;
		}
		return 'Queue capacity is full.';
	}

	dequeue(){
		if(this._dequeue.length <= 0){
			while(this._enqueue > 0){
				this._dequeue.push(this._enqueue[0]);
				this._enqueue.shift();
			}
		}
		this._dequeue.shift();
	}

	peek(){
		if(this._dequeue.length <= 0){
			if(this._enqueue.length > 0){
				return this._enqueue[0];
			}
			return 'Queue is empty';
		}

		return this._dequeue[0];
	}

	count(){
		return this._enqueue.length + this._dequeue.length;
	}

	contains(element){
		for(let i=0; i<this._enqueue.length; i++){
			if(this._enqueue[i]===element) return true;
		}
		for(let i=0; i<this._dequeue.length; i++){
			if(this._dequeue[i]===element) return true;
		}

		return false;
	}
}