Formatting windows product keys dynamically

I am working on a project and they want to have the product keys automatically add the dashes and capitalize the key. The following code will work for that as long as you type the product key all at once and do not have to edit anything in the middle. My question is how would you "properly" format the product key in: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx.

Code:

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function productKey(data, e) {
  // Get the product key you are typing
  var productKey = data.value;
  // Capture the code for the key just pressed
  var KeyID = (window.event) ? event.keyCode : e.keyCode;
  // Capitalize the product key
  productKey = productKey.toUpperCase();
  // Find the key length
  var keyLength = productKey.length;
  switch(KeyID) {
    case 8: // Backspace key was pressed
      // Determine if we need to remove an extra character due to
      // removing the slash that we automatically added
      switch(keyLength % 6) {
        case 5:
          if(keyLength>4) {
            // Delete one extra character
            productKey = productKey.substr(0, (keyLength-1));
          }
          break;
      }     
      break;
    default:
      // Determine if we need to add a - or not
      switch(keyLength % 6) {
        case 5: // We just typed the 5th character in the 6th character string (including the -)
          if(keyLength<29) {
            // Add a - to the end of the product key
            productKey = productKey+'-';
          }
          break;
      }
      break;
  }
  document.getElementById(data.id).value = productKey;
}

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Then a textbox like:

Code:

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<input type="text" name="key" id="key" onKeyUp="productKey(this, event)" value="" size="40">

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Any ideas?

The solution is simpler than using "window.event" to catch the key presses. Simply use the onkeypress event.

Code:

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window.onload = function() {
  document.getElementById('field_1').keypress = format_keys;
}

function format_keys ()
{
  // make input uppercase, and add dash after every x number of characters
}

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You also can just use onchange or onblur event, especially if using onkeypress slows down typing response.