如何使用JavaScript检查下拉值

Question

I have drop-down and Textbox inside a Gridview so I want to check the followings on a button click: (1) Check if NOTHING is selected from the drop down first (the drop-down options are either YES, NO or NA) . If nothing is selected, I want to show message that reads like this “Please make selection from the drop-down” (2) If the selection from the drop-down is NO and the Textbox is blank or empty then I want to show message that says: “Please provide comments”

The first code checks if the text-box is blank and it works and the 2nd code checks if no selection is made from the drop down and that one works fine too so how can i combine between those 2 codes? I want to execute both codes on button click, right now it is only calling the first code. please help. Thanks. here is my code that checks if the textbox is blank:

<script type ="text/javascript">
    function Validate() {
        var flag = false;
        var gridView = document.getElementById('<%= GridView1.ClientID %>');

        for (var i = 1; i < gridView.rows.length; i++) {
            var selects = gridView.rows[i].getElementsByTagName('select');
            var areas = gridView.rows[i].getElementsByTagName('textarea');
            if (selects != null && areas != null) {
                if (areas[0].type == "textarea") {
                    var txtval = areas[0].value;
                    var selectval = selects[0].value;
                    if (selectval == "No" && (txtval == "" || txtval == null)) {

                        flag = false;
                        break;
                    }
                    else {
                        flag = true;
                        document.getElementById('<%=btnSubmit.ClientID%>').style.visibility = 'visible';
                    }
                }
            }
        }
        if (!flag) {
            alert('Please note that comments are required if you select "No" from the dropdown box.  Thanks');
            document.getElementById('<%=btnSubmit.ClientID%>').style.visibility = 'hidden';
        }
        return flag;
    }
</script>

and here is the code that checks the drop-down

<script type="text/javascript">
      function validate_DD() {
          var flag = true;
          var dropdowns = new Array(); //Create array to hold all the dropdown lists.
          var gridview = document.getElementById('<%=GridView1.ClientID%>'); //GridView1 is the id of ur gridview.
          dropdowns = gridview.getElementsByTagName('Select'); //Get all dropdown lists contained in GridView1.
          for (var i = 0; i < dropdowns.length; i++) {
              if (dropdowns.item(i).value == 'Select') //If dropdown has no selected value
              {
                  flag = false;
                  break; //break the loop as there is no need to check further.
              }
          }
          if (!flag) {
              alert('Please select either Yes, No or NA in each dropdown and click the Save button again.  Thanks');
              document.getElementById('<%=btnSubmit.ClientID%>').style.visibility = 'hidden';

          }

          return flag;

      }
</script>

Answer 1

Try this:

<select id="ddlCars">
  <option value="1">Honda</option>
  <option value="2" selected="selected">Toyota</option>
  <option value="3">BMW</option>
</select>

Accessing dropdown:

To get the value:
var el = document.getElementById("ddlCars");
var val = el.options[el.selectedIndex].value; // val will be 2

To get the text:
var el = document.getElementById("ddlCars");
var car = el.options[el.selectedIndex].text; //car will be Toyota