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/**
 * Auto update cart after quantity change
 *
 * @return  string
 **/
add_action( 'wp_footer', 'cart_update_qty_script' );
function cart_update_qty_script() {
  if (is_cart()) :
   ?>
    <script>
    	var reloadTime;

        $('div.woocommerce').on('change, input', '.qty', function(){
           $("[name='update_cart']").removeAttr('disabled');
           	clearTimeout(reloadTime);
           	reloadTime = setTimeout(function(){ 
           		$("[name='update_cart']").trigger("click"); 
       		}, 1000);
        });

   </script>
<?php
endif;
}