检查下拉选择的选项是否不是JavaScript的第一个选项 [英] Check if dropdown's selected option is not the first with JavaScript

问题描述

以下是我在HTML代码中的选项：

 < label id =subn> 
< select name =subsid =subs> 
< option value =nothing>选择主题< / option> 
< option value =一般问题>一般问题< / option> 
< option value =MemberShip Area> MemberShip Area< / option> 
< option value =其他>其他< / option> 
< / select> 
< / label> 
  

我想要创建JavaScript代码来检查用户是否选择了第一个选项。 / p>

这是我试过的：

  if（document.getElementsByTagName 'option'）==nothing）{
 document.getElementById（subn）。innerHTML =Subject is Required！; 
 document.getElementById（subs）。focus（）; 
返回false; 
 
  

解决方案

nothing 将会是第一个（通常是我的经历）：

  if（document.getElementById（'subs'）。selectedIndex == 0）{
  

比较基于值，做到这一点：

  var sel = document.getElementById（'subs'）; 
 if（sel.options [sel.selectedIndex] .value =='nothing'）{
  

<

 < select name =subs你可以改变你的标记，使标签在旁边，如下所示： id =subs>< / select>< label id =subnfor =subs>< / label> 
  

否则这部分： .innerHTML =Subject is Required！; 会清除你的< select> ：）

Below are the options that i have in my HTML code:

    <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.

Here is what I tried:

if (document.getElementsByTagName('option') == "nothing"){
    document.getElementById("subn").innerHTML = "Subject is Required!";
    document.getElementById("subs").focus();
    return false;
}

解决方案

You can check like this if nothing is going to be first (usually the case in my experience):

if (document.getElementById('subs').selectedIndex == 0){

To still compare based on the value, do this:

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:

<select name="subs" id="subs"></select><label id="subn" for="subs"></label>

Otherwise this part: .innerHTML = "Subject is Required!"; will erase your <select> :)

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