检查下拉列表的选定选项是否不是第一个使用 JavaScript
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Check if dropdown's selected option is not the first with JavaScript
提问by Mahmoud
Below are the options that i have in my HTML code:
以下是我在 HTML 代码中的选项：
<label id="subn">
<select name="subs" id="subs">
<option value="nothing">Choose a Subject</option>
<option value="General Question">General Question</option>
<option value="MemberShip Area">MemberShip Area</option>
<option value="Others">Others</option>
</select>
</label>
I want to create JavaScript code that will check if the user selected an option other than the first.
我想创建 JavaScript 代码来检查用户是否选择了第一个以外的选项。
Here is what I tried:
这是我尝试过的：
if (document.getElementsByTagName('option') == "nothing"){
document.getElementById("subn").innerHTML = "Subject is Required!";
document.getElementById("subs").focus();
return false;
}
回答by Nick Craver
You can check like this if nothingis going to be first (usually the case in my experience):
您可以像这样检查是否nothing要首先（根据我的经验通常是这种情况）：
if (document.getElementById('subs').selectedIndex == 0){
To still compare based on the value, do this:
要仍然根据值进行比较，请执行以下操作：
var sel = document.getElementById('subs');
if (sel.options[sel.selectedIndex].value == 'nothing') {
You may wand to change your markup so the label is beside, like this:
你可能想改变你的标记，这样标签就在旁边，像这样：
<select name="subs" id="subs"></select><label id="subn" for="subs"></label>
Otherwise this part: .innerHTML = "Subject is Required!";will erase your <select>:)
否则这部分：.innerHTML = "Subject is Required!";将删除您的<select>:)
回答by Sarfraz
This should do it:
这应该这样做：
var index = document.your_form_name.subs.selectedIndex;
var value = document.your_form_name.subs.options[index].value;
if (value === "nothing"){
// your further code here.........
}
回答by RoToRa
document.getElementsByTagName('option')gives a collection of all optionelements in the document and "nothing"is a string. Comparing a collection to a string is quite useless.
document.getElementsByTagName('option')给出option文档中所有元素的集合，"nothing"是一个字符串。将集合与字符串进行比较是非常无用的。
Also setting document.getElementById("subn").innerHTML = "Subject is Required!";will delete the selectelement, so document.getElementById("subs")wouldn't find anything any more.
设置document.getElementById("subn").innerHTML = "Subject is Required!";也会删除select元素，所以document.getElementById("subs")不会再找到任何东西。
If you just need to know if anything is selected check the selectedIndexproperty of the selectelement:
如果您只需要知道是否选择了任何内容，请检查元素的selectedIndex属性select：
if (document.getElementById("subs").selectedIndex <= 0) {
// nothing is selected
}
EDIT:Changed > 0to <= 0. I would assume that it should be checked if the user didn't select anything, too.
编辑：更改> 0为<= 0. 我认为如果用户没有选择任何内容，也应该检查它。
