show div depending on select option

Oh help, I've tried it a million different ways yet it still does not work: If you select update or final from a select/option box, it should show the div that has an input field in it. It only does what the default shows in the switch statement. Of course, it's only after a selection is made that I want it to determine whether it shows the input field or not.

in head section...

$(document).ready(function(){  
$('#needfilenum').hide();  
var optionValue = $("#needtoshow").val();  

switch (optionValue)  
{  
case 'update':  
$("#needfilenum").show();
break;  

case 'final':  
$("#needfilenum").show();  
break;  
default:  
$("#needfilenum").hide();  
break;  
    }
});
//});

'<select id="needtoshow" >  
<option id="dfaut" value="0">Select Something</option>
<option id="update" value="update">Update</option>
<option id="final" value="final">Final</option>
<option id="allergy"valu开发者_如何学Goe="allergy">Vegan</option>  
</select>
<div id="needfilenum"  style="background:#f00;">  
<input type="text" name="wharever"   />
</div>  

I can change the default on the switch and that seems to dictate what it shows also tried

//  $("#needtoshow").change(function() {  

//      switch ($(this).val())

---

If you want to have the div show and hide when the drop-down changes, you need to bind to the change event, for example:

$(document).ready(function() {
  $('#needfilenum').hide();

  $('#needtoshow').bind('change', function() {
    var optionValue = $("#needtoshow").val();

    switch (optionValue)
    {
      case 'update':
      case 'final':
        $("#needfilenum").show();
        break;

      default:
        $("#needfilenum").hide();
        break;
    }
  });
});

In your code, the switch statement runs only once when the page first loads.

---

You probably want to bind an event listener on your select box. (change event) So you would have something along the lines of:

$("#oldfilenum").change(function() {
  var optionValue = $(this).val();
  switch (optionValue) { 
    case 'update': 
      $("#needfilenum").show(); 
      break; 
    case 'final ': 
      $("#needfilenum").show(); 
      break; 
    default: 
      $("#needfilenum").hide(); 
  } 
};

---

Try something like this:

var selectBox = $("#oldfilenum"), magicDiv = $("#needfilenum");
selectBox.bind("change", function() {
    var val = this.value;
    if (val === "update" || val === "final") {
        magicDiv.show();
    } else {
        magicDiv.hide();
    }
});

Of course you can use switch instead, or have a [] of acceptable values and do it.indexOf(val) > -1 or whatever.

As Victor commented on another answer, change fires on blur in MSIE, so you may want to use another event if that is an issue, perhaps mouseup.

---

You should look into the change() event. Attach that to your <select> and then perform your logic.

---

Your checking function runs only once, and not every time you change the select field. You need to put an onchange handler into the select field:

<select id="needtoshow" onchange="your_function_name_here()">