Based on semantics, both drop-down boxes and text boxes can be input

<div class="field "><%= select_tag "quantity", options_for_select( %w(100g  250g 500g 500ml 1kg 1L 2.5L 5kg 5L 10kg 10L).unshift(@chemical_info[:quantity]).uniq, @chemical_info[:quantity]), include_blank: "选择数量", class: 'ui search fluid dropdown J_quantity' %></div>

$('.J_quantity').dropdown({
    allowAdditions: true,
    onChange: function(val) {
      var tag_id = $("#tag_id").val();
      var quantity = val;
      window.location.href = '/admin/print/whmall_tags/print?tag_id='+tag_id+"&inventory_id="+"<%= @chemical_info[:from_id] %>"+"&quantity="+quantity ;
    }
});


allowAdditions: true works similarly:
The drop-down box is optional and can be filled in
$('.J_quantity').find('input').removeAttr('readonly');