If you have a form that limits characters entered into a textfield, using this simple approach you can automatically jump to the next control, making it easy for your user

Say you have a zip code field that takes in 5 numbers, next you have a state dropdown.  Your user should be able to type in the 5 digit zip code, then boom, the focus is automatically shifts to the dropdown.  It is very simple to implement.  It just requires the following JS function:

function next(currentControl, maxLength, nextControl)
   {
    if(document.getElementById(currentControl).value.length >= maxLength)
    document.getElementById(nextControl).focus();
  }

and then just call this from a textbox in html:

<input id="Text1" onkeyup="next('Text1', '5', 'Text2')" type="text" />

Or if you are using an asp.net TextBox control:

txt1.Attributes.Add("onkeyup", "next('txt1','5','txt2')");

it's just that easy... here is an example using both asp.net and just html: