Quantity Dropdown Instead of a Number Box

$wpide_qty_options = 20; // Highest option when the product has no maximum.

add_action( 'wp_footer', function () use ( $wpide_qty_options ) {
    if ( ! function_exists( 'is_product' ) || ! ( is_product() || is_cart() ) ) {
        return;
    }
    ?>
    <script>
    ( function () {
        var cap = <?php echo (int) $wpide_qty_options; ?>;
        function convert( root ) {
            root.querySelectorAll( 'input.qty[type="number"]:not([data-wpide])' ).forEach( function ( input ) {
                var min = parseFloat( input.min ) || 1, step = parseFloat( input.step ) || 1;
                var max = parseFloat( input.max ) || 0;
                if ( input.type === 'hidden' || ( max && max <= min ) ) { return; }
                var limit = max ? Math.min( max, min + step * ( cap - 1 ) ) : min + step * ( cap - 1 );
                var current = parseFloat( input.value ) || min;
                var select = document.createElement( 'select' );
                select.name = input.name;
                select.id = input.id;
                select.className = input.className;
                select.setAttribute( 'aria-label', input.getAttribute( 'aria-label' ) || 'Quantity' );
                for ( var q = min; q <= limit; q += step ) { select.add( new Option( q, q, false, q === current ) ); }
                if ( current > limit ) { select.add( new Option( current, current, true, true ) ); }
                input.setAttribute( 'data-wpide', '1' );
                select.addEventListener( 'change', function () { select.dispatchEvent( new Event( 'input', { bubbles: true } ) ); } );
                input.parentNode.replaceChild( select, input );
            } );
        }
        convert( document );
        if ( window.jQuery ) { jQuery( document.body ).on( 'updated_cart_totals', function () { convert( document ); } ); }
    } )();
    </script>
    <?php
} );