Add plus and minus buttons to WooCommerce quantity inputs

kia_add_script_to_footer.php

// Add this to your theme's functions.php
function kia_add_script_to_footer(){
    if( ! is_admin() ) { ?>
    <script>
    jQuery(document).ready(function($){
    $('.quantity').on('click', '.plus', function(e) {
        $input = $(this).prev('input.qty');
        var val = parseInt($input.val());
        var step = $input.attr('step');
        step = 'undefined' !== typeof(step) ? parseInt(step) : 1;
        $input.val( val + step ).change();
    });

    $('.quantity').on('click', '.minus', 
        function(e) {
        $input = $(this).next('input.qty');
        var val = parseInt($input.val());
        var step = $input.attr('step');
        step = 'undefined' !== typeof(step) ? parseInt(step) : 1;
        if (val > 0) {
            $input.val( val - step ).change();
        } 
    });
});
</script>
<?php }
}
add_action( 'wp_footer', 'kia_add_script_to_footer' );

quantity-input.php

<?php
/**
 * Product quantity inputs with plus/minus buttons
 *
 * Save this template to your theme as woocommerce/global/quantity-input.php.
 *
 * HOWEVER, on occasion WooCommerce will need to update template files and you
 * (the theme developer) will need to copy the new files to your theme to
 * maintain compatibility. We try to do this as little as possible, but it does
 * happen. When this occurs the version of the template file will be bumped and
 * the readme will list any important changes.
 *
 * @see 	    https://docs.woocommerce.com/document/template-structure/
 * @author 		WooThemes
 * @package 	WooCommerce/Templates
 * @version     2.5.0
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly
}

if ( $max_value && $min_value === $max_value ) {
	?>
	<input type="hidden" name="<?php echo esc_attr( $input_name ); ?>" value="<?php echo esc_attr( $min_value ); ?>" />
	<?php
} else {
	?>
	<div class="quantity">
		<input class="minus" type="button" value="-">
		<input type="number" step="<?php echo esc_attr( $step ); ?>" min="<?php echo esc_attr( $min_value ); ?>" max="<?php echo esc_attr( 0 < $max_value ? $max_value : '' ); ?>" name="<?php echo esc_attr( $input_name ); ?>" value="<?php echo esc_attr( $input_value ); ?>" title="<?php echo esc_attr_x( 'Qty', 'Product quantity input tooltip', 'woocommerce' ) ?>" class="input-text qty text" size="4" pattern="<?php echo esc_attr( $pattern ); ?>" inputmode="<?php echo esc_attr( $inputmode ); ?>" />
		<input class="plus" type="button" value="+">
	</div>
	<?php
}