JavaScript - how to implement queue
In this short article, we would like to show how to use JavaScript built-in queues.
In JavaScript, the queue data structure is combined with Array. There are available push, pop, shuft and unshift methods that we can use as enqueue and dequeue methods.
Methods usage in variants:
push(...)as enqueue andshift()as dequeue,unshift(...)as enqueue andpop()as dequeue.
Check the below examples to know more about how it works.
Let's suppose we want to queue and dequeue: A, B and C.
To do it we need to call 3 times push(...) and later 3 times shift().
Simple example:
xxxxxxxxxxvar queue = [ ]; // new Array()queue.push('A'); // enqueue Aqueue.push('B'); // enqueue Bqueue.push('C'); // enqueue Cconsole.log('Queue contains: ' + queue.join(', '));console.log(queue.shift()); // dequeue Aconsole.log(queue.shift()); // dequeue Bconsole.log(queue.shift()); // dequeue Cconsole.log('Queue contains: ' + queue.join(', '));This kind of queue works the same way but keeps items in reversed order - in the first example printing for filled queue returned A, B, C, so in this example it will be C, B, A.
To enqueue items we use unshift method that puts items at beginning of the queue.
To dequeue items we use pop method that removes items from the end of the queue.
Simple example:
xxxxxxxxxxvar queue = [ ]; // new Array()queue.unshift('A'); // enqueue Aqueue.unshift('B'); // enqueue Bqueue.unshift('C'); // enqueue Cconsole.log('Queue contains: ' + queue.join(', '));console.log(queue.pop()); // dequeue Aconsole.log(queue.pop()); // dequeue Bconsole.log(queue.pop()); // dequeue Cconsole.log('Queue contains: ' + queue.join(', '));We are able to insert many items during one enqueue operation.
Variant 1 - simple example:
xxxxxxxxxxvar queue = [ ]; // new Array()queue.push('A', 'B', 'C'); // enqueue A, B and Cconsole.log('Queue contains: ' + queue.join(', '));console.log(queue.shift()); // dequeue Aconsole.log(queue.shift()); // dequeue Bconsole.log(queue.shift()); // dequeue Cconsole.log('Queue contains: ' + queue.join(', '));Variant 2 - simple example:
Hint: be careful to use it becouse it changed enqueue ordering and can lead to mistakes.
xxxxxxxxxxvar queue = [ ]; // new Array()queue.unshift('A', 'B', 'C'); // enqueue A, B and Cconsole.log('Queue contains: ' + queue.join(', '));console.log(queue.pop()); // dequeue Aconsole.log(queue.pop()); // dequeue Bconsole.log(queue.pop()); // dequeue Cconsole.log('Queue contains: ' + queue.join(', '));