jQuery Counter with Next and Previous Buttons

How to increment or decrement a form field using jQuery, specially useful for quantity fields.

HTML

<button class='prev' field='quantity'>Prev</button>
<span>1</span>/5
<button class='next' field='quantity'>Next</button>

JavaScript

jQuery(document).ready(function(){
    // This button will increment the value
    $('.next').click(function(e){
        // Stop acting like a button
        e.preventDefault();
        // Get the field name
        fieldName = $(this).attr('field');
        // Get its current value
        var currentVal = parseInt($('span').html());
        // If is not undefined
        if (currentVal == 5) {
            $('span').html(currentVal);
        }
        else if (!isNaN(currentVal) ) {
            // Increment
            $('span').html(currentVal + 1);
        } 
        else {
            // Otherwise put a 0 there
            $('span').html(0);
        }
    });
    // This button will decrement the value till 0
    $(".prev").click(function(e) {
        // Stop acting like a button
        e.preventDefault();
        // Get the field name
        fieldName = $(this).attr('field');
        // Get its current value
        var currentVal = parseInt($('span').html());
        // If it isn't undefined or its greater than 0
        if (!isNaN(currentVal) && currentVal > 0) {
            // Decrement one
            $('span').html(currentVal - 1);
        } else {
            // Otherwise put a 0 there
            $('span').html(0);
        }
    });
});