我的代码URL输出是不正确的

我正在使用Shopify，并且使用当前代码，我希望根据用户在下拉菜单中的选择将用户重定向到正确的URL。

我为下拉菜单编写了以下代码:

    <ul class="clearfix filters">
    <li class="clearfix filter">
    <label>Shop by color</label>
    <select class="coll-filter">
    <option value="/collections/all">All</option>
    {% for col in collections %}
    <option value="{{ col.url }}"{% if collection.handle == col.handle %}selected="selected"{% endif %}>{{ col.title }}</option>
{% endfor %}
    </select>
    </li>
    </ul>

<script>
  Shopify.queryParams = {};
  if (location.search.length) {
    for (var aKeyValue, i = 0, aCouples = location.search.substr(1).split('&'); i < aCouples.length; i++) {
      aKeyValue = aCouples[i].split('=');
      if (aKeyValue.length > 1) {
        Shopify.queryParams[decodeURIComponent(aKeyValue[0])] = decodeURIComponent(aKeyValue[1]);
      }
    }
  }
  var collFilters = jQuery('.coll-filter');
  collFilters.change(function() {
      var newTags = [];
      var newURL = '';
      collFilters.each(function() { 
        if (jQuery(this).val()) {
          newTags.push(jQuery(this).val());
        }
      });
      {% if collection.handle %}
      newURL = '{{ collection.handle }}';
      if (newTags.length) {
        newURL += '/' + newTags.join('+');
      }
      var search = jQuery.param(Shopify.queryParams);
      if (search.length) {
        newURL += '?' + search;
      }
      location.href = newURL;    
      {% else %}
      if (newTags.length) {
        Shopify.queryParams.constraint = newTags.join('+');        
      }
      else {
        delete Shopify.queryParams.constraint;
      }
      location.search = jQuery.param(Shopify.queryParams);
      {% endif %}      
  });
</script>

代码的作用是输出如下:http://domain.com/collections/all//collections/product

但我需要的是:http://domain.com/collections/product

问题应该在这部分(位置)。href = newURL;)，但我不能使它正常工作。