基于下拉菜单值的 Javascript if 语句

Question

我对js中的if语句有疑问。我做了一个声明，但它似乎不起作用。我想通过单击“按钮 1”来检查这些语句。脚本是在我计算总数之前检查是否有任何运输成本。 谁能告诉我如何解决我的问题？

这是我的脚本:

<SCRIPT TYPE="text/javascript">
function berekeningen()
{

if (document.getElementById("DropdownMenu1").value = "Eeklo" && document.getElementById("Order_Subtotal").firstChild.data >= 20)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Adegem" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Kaprijke" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Lembeke" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Oosteeklo" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Sint-Laureins" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Ursel" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Waarschoot" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Zomergem" && document.getElementById("Order_Subtotal").firstChild.data >= 25)
  {
  document.getElementById("Transportation_Cost").value="0.00";
  }
else
  {
  document.getElementById("Transportation_Cost").value="3.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Knesselare")
  {
  document.getElementById("Transportation_Cost").value="5.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Lovendegem")
  {
  document.getElementById("Transportation_Cost").value="5.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Bassevelde")
  {
  document.getElementById("Transportation_Cost").value="5.00";
  }

if  (document.getElementById("DropdownMenu1").value = "Maldegem")
  {
  document.getElementById("Transportation_Cost").value="5.00";
  }
}
</SCRIPT>

编辑: 我用变量稍微更改了脚本，但它不起作用

<script type="text/javascript" src="http://code.jquery.com/jquery-1.8.0.js"></script>

<SCRIPT TYPE="text/javascript">
function berekeningen()
{
   var plaats           = document.getElementById("plaats").value;
   var kosten           = document.getElementById("kosten").value;
   var subtotaal        = document.getElementById("Bestelling_subtotaal").firstChild.data
   var class_1_plaatsen = new Array("Eeklo");
   var class_2_plaatsen = new Array("Adegem", "Kaprijke", "Lembeke", "Oosteeklo",
                                    "Sint-Laureins", "Ursel", "Waarschoot", "Zomergem");
   var class_3_plaatsen = new Array("Knesselare", "Lovendegem", "Bassevelde", "Maldegem");

   if ($.inArray(plaats, class_1_plaatsen) >= 0) {

      // Berekening voor plaatsen in prijscategorie 1 hieronder.

   }
   else if ($.inArray(plaats, class_2_plaatsen) >= 0) {

      // Berekening voor plaatsen in prijscategorie 2 hieronder.

   }
   else {

      // Berekening voor overige plaatsen hieronder.

   }
}
</SCRIPT>

我不想做这个:

When var plaats = class_1_plaatsen and subtotaal < 15, then alert (We leveren vanaf minimum € 15). But if subtotaal is between 15 and 20, then kosten = 3. But if subtotaal >= 20, then kosten = 0.

When var plaats = class_2_plaatsen and subtotaal < 20, then alert (We leveren vanaf minimum € 20). But if subtotaal is between 20 and 25, then kosten = 3. But if subtotaal >= 25, then kosten = 0.

When var plaats = class_3_plaatsen and subtotaal < 20, then alert (We leveren vanaf minimum € 20). But if subtotaal >= 20, then kosten = 5.

活力

Answer 1

不应该你所有的 if 语句都有两个 ==

if  (document.getElementById("DropdownMenu1").value == "Knesselare")