javascript 选择标签中的 onchange 事件！
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onchange event in select tag!
提问by Shilpa
The following code should give me a 1 in ParentSelect if I change the option in the menu, but I am getting a 0. Can anyone tell me what is the error?
如果我更改菜单中的选项，下面的代码应该在 ParentSelect 中给我一个 1，但我得到一个 0。谁能告诉我错误是什么？
<input type="hidden" name="ParentSelect" value="0" />
<select class="style" onchange="document.forms[0].elements['ParentSelect']=1" >
<option value="NULL">NULL</option>
...
</select>
Here, I have two tables in the database. They contain some fields like ServerName, etc..
在这里，我在数据库中有两个表。它们包含一些字段，如 ServerName 等。
Suggestions?
建议？
回答by Chris Baker
You are directly assigning the value 1to the property document.forms[0].elements['ParentSelect'], whereas you presumably mean to change the value of the element, which would be achieved like this:
您直接将值分配给1property document.forms[0].elements['ParentSelect']，而您大概是想更改元素的值，这将像这样实现：
document.forms[0].elements['ParentSelect'].value = 1
document.forms[0].elements['ParentSelect'].value = 1
I agree with some of the other comments concerning the lack of valid HTML strucutre, and I would add that if you are going to reference the field via document.forms[0], you may as well give the field an id property so you can simply use 'document.getElementById` so your code works regardless of the other forms on the page. Anyway, using your method, here is the complete code:
我同意其他一些关于缺少有效 HTML 结构的评论，我想补充一点，如果您要通过 引用该字段document.forms[0]，您也可以为该字段指定一个 id 属性，以便您可以简单地使用 'document.getElementById ` 所以无论页面上的其他表单如何，您的代码都可以正常工作。无论如何，使用您的方法，这是完整的代码：
<form>
<input type="hidden" name="ParentSelect" value="0" />
<select class="style" onchange="document.forms[0].elements['ParentSelect'].value=1" >
<option value="1">Value 1</option>
<option value="2">Value 2</option>
</select>
</form>
Using an id instead:
使用 id 代替：
<form>
<input id="parentSelect" type="hidden" name="ParentSelect" value="0" />
<select class="style" onchange="var e = document.getElementById('parentSelect'); if (e) e.value=1;" >
<option value="1">Value 1</option>
<option value="2">Value 2</option>
</select>
</form>
回答by dev-null-dweller
document.forms[0].elements['ParentSelect']returns whole input, if you want to set it's value use
document.forms[0].elements['ParentSelect']返回整个输入，如果你想设置它的值使用
document.forms[0].elements['ParentSelect'].value = 1
