How to check if an item is selected from an HTML drop down list?

问题

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

Below is my HTML Code :

<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 :

var card = document.getElementByName("cards")[0].value;
if (card.value == selectcard) {
    alert("Please select a card type");
}

回答1:

Well you missed quotation mark around your string selectcard it should be "selectcard"

if (card.value == selectcard)

should be

if (card.value == "selectcard")

Here is complete code for that

function validate()
{
 var ddl = document.getElementById("cardtype");
 var selectedValue = ddl.options[ddl.selectedIndex].value;
    if (selectedValue == "selectcard")
   {
    alert("Please select a card type");
   }
}

JS Fiddle Demo

回答2:

<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3:

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

<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.

回答4:

You can check if the index of the selected value is 0 or -1 using the selectedIndex property.

In your case 0 is also not a valid index value because its the "placeholder":
<option value="selectcard">--- Please select ---</option>

LIVE DEMO

function Validate()
 {
   var combo = document.getElementById("cardtype");
   if(combo.selectedIndex <=0)
    {
      alert("Please Select Valid Value");
    }
 }

回答5:

<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>

回答6:

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.

<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7:

Select select = new Select(_element);
List<WebElement> selectedOptions = select.getAllSelectedOptions();

if(selectedOptions.size() > 0){
    return true;
}else{
    return false;
}

来源：https://stackoverflow.com/questions/15987140/how-to-check-if-an-item-is-selected-from-an-html-drop-down-list