WooCommerce Quantity Increment (quantity-increment-buttons-for-woocommerce) free WordPress plugin

WooCommerce uses number inputs for the cart quantities by default, as most browsers now support <input type="number" />.

However, you may want to have JavaScript powered inputs if you want greater control over appearance. Simply install and activate this plugin to do so.

It optionally includes a Number Polyfill, which is a polyfill for implementing the HTML5 <input type="number"> element in browsers that do not currently support it.

To include this, add the following code to your theme’s functions.php file:

add_action( 'wp_enqueue_scripts', 'wcqi_enqueue_polyfill' );
function wcqi_enqueue_polyfill() {
    wp_enqueue_script( 'wcqi-number-polyfill' );
}