如何检查是否从 HTML 下拉列表中选择了一个项目？
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How to check if an item is selected from an HTML drop down list?
提问by littledevils326
I have a drop drown list and I am having trouble checking whether or not a value has been selected from the drop down list
我有一个下拉列表，但无法检查是否从下拉列表中选择了一个值
Below is my HTML Code :
下面是我的 HTML 代码：
<label class="paylabel" for="cardtype">Card Type:</label>
<select id="cardtype" name="cards">
<option value="selectcard">--- Please select ---</option>
<option value="mastercard">Mastercard</option>
<option value="maestro">Maestro</option>
<option value="solo">Solo (UK only)</option>
<option value="visaelectron">Visa Electron</option>
<option value="visadebit">Visa Debit</option>
</select><br/>
Below is my JavaScript Code :
下面是我的 JavaScript 代码：
var card = document.getElementByName("cards")[0].value;
if (card.value == selectcard) {
alert("Please select a card type");
}
回答by Sachin
Well you missed quotation mark around your string selectcardit should be "selectcard"
好吧，您错过了字符串周围的引号，selectcard它应该是"selectcard"
if (card.value == selectcard)
should be
应该
if (card.value == "selectcard")
Here is complete code for that
这是完整的代码
function validate()
{
var ddl = document.getElementById("cardtype");
var selectedValue = ddl.options[ddl.selectedIndex].value;
if (selectedValue == "selectcard")
{
alert("Please select a card type");
}
}
回答by Ashish Chopra
<script>
var card = document.getElementById("cardtype");
if(card.selectedIndex == 0) {
alert('select one answer');
}
else {
var selectedText = card.options[card.selectedIndex].text;
alert(selectedText);
}
</script>
回答by Jay.D
function check(selId) {
var sel = document.getElementById(selId);
var dropDown_sel = sel.options[sel.selectedIndex].text;
if (dropDown_sel != "none") {
state=1;
//state is a Global variable initially it is set to 0
}
}
function checkstatevalue() {
if (state==1) {
return 1;
}
return false;
}
and html is for example
和 html 是例如
<form name="droptest" onSubmit="return checkstatevalue()">
<select id='Sel1' onchange='check("Sel1");'>
<option value='junaid'>Junaid</option>
<option value='none'>none</option>
<option value='ali'>Ali</option>
</select>
</form>
Now when submitting a form first check what is the value of state if it is 0 it means that no item has been selected.
现在，当提交表单时，首先检查 state 的值是多少，如果它是 0，则表示没有选择任何项目。
回答by jonathana
You can check if the index of the selected value is 0 or -1 using the selectedIndexproperty.
您可以使用该selectedIndex属性检查所选值的索引是 0 还是 -1 。
In your case 0 is also not a valid index value because its the "placeholder":<option value="selectcard">--- Please select ---</option>
在您的情况下 0 也不是有效的索引值，因为它是“占位符”：<option value="selectcard">--- Please select ---</option>
function Validate()
{
var combo = document.getElementById("cardtype");
if(combo.selectedIndex <=0)
{
alert("Please Select Valid Value");
}
}
回答by RamseyTech
I believe this is the most simple in all aspects unless you call the validate function be other means. With no/null/empty value to your first option is easier to validate. You could also eliminate the first option and start with the most popular card type.
我相信这在各方面都是最简单的，除非您以其他方式调用验证函数。使用 no/null/empty 值作为您的第一个选项更容易验证。您也可以取消第一个选项并从最流行的卡片类型开始。
<form name="myForm">
<select id="cardtype" name="cards">
<option value="">--- Please select ---</option>
<option value="mastercard" selected="selected">Mastercard</option>
<option value="maestro">Maestro</option>
<option value="solo">Solo (UK only)</option>
<option value="visaelectron">Visa Electron</option>
<option value="visadebit">Visa Debit</option>
</select><br />
<input type="submit" name="submit" class="button" value="SUBMIT" onmouseover="validate()"></form>
<script>
function validate() {
if (document.myform.cards.value == "") {
alert("Please select a card type");
document.myForm.cards.focus();
}
</script>
回答by Dominic Giallombardo
Select select = new Select(_element);
List<WebElement> selectedOptions = select.getAllSelectedOptions();
if(selectedOptions.size() > 0){
return true;
}else{
return false;
}
回答by Phillipe Rosário
<label class="paylabel" for="cardtype">Card Type:</label>
<select id="cardtype" name="cards">
<option value="selectcard">--- Please select ---</option>
<option value="mastercard" selected="selected">Mastercard</option>
<option value="maestro">Maestro</option>
<option value="solo">Solo (UK only)</option>
<option value="visaelectron">Visa Electron</option>
<option value="visadebit">Visa Debit</option>
</select><br />
<script>
var card = document.getElementById("cardtype");
if (card.options[card.selectedIndex].value == 'selectcard') {
alert("Please select a card type");
return false;
}
</script>
