fill the textbox on change of a dropdown value selected using javascript

you need to write Html code similar as:

<select Id="myDropdown">
    <option>1</option>
    <option>2</option>
    <option>3</option>
</select>

<input id="txtBox" type="text">

jQuery Code as:

$("#myDropdown").change(function () {
    var selectedValue = $(this).val();
    $("#txtBox").val($(this).find("option:selected").attr("value"))
});

[Edit member="Tadit"]
Removed extra pre tags.
Formatted texts.
[/Edit]

you can try this

function chkind(){
   var dropdown1 = document.getElementById('dropdown1');
   var textbox = document.getElementById('textbox');
   if(dropdown1.selectedIndex == 0){
     textbox.value = "hi";
   } else if(dropdown1.selectedIndex == 1) {
     textbox.value = "bye";
   }
   }

try this also to get index value
var a = dropdown1.options[dropdown1.selectedIndex].value;

like this

function chkind(){
   var dropdown1 = document.getElementById('dropdown1');
   var a = dropdown1.options[dropdown1.selectedIndex].value;
   var textbox = document.getElementById('textbox');
     textbox.value = a;  
   }