how to use innerHTML here.

[saurabhkerkar]

hey guys in this code i have 4 textboxes in a form:
1: invoice no:
2: invoice date:
3: challan no:
4: challan date:

[DONT WORRY ABOUT THIS "CHALLAN" WORD ITS AN INDIAN WORD!!!]

[now the requirement is that when i enter invoice no it should come automatically into the challan no field
and same for the date field also ]

I think innerHTML will be used but very confused about the scriptcan u help me out????

<form name="form1" method="post" action="">
Invoice No:&nbsp;
<input name="textfield4" id="totalvalue" type="text" size="25" maxlength="25" border="0">&nbsp;
Invoice Date:&nbsp;<input name="textfield4" id="totaldatevalue" type="text" size="25" maxlength="25" border="0">
Challan No: &nbsp;
<input name="textfield4" id="subtotalvalue" type="text" size="25" maxlength="25" border="0">
Challan Date:<input name="textfield4" id="subtotaldatevalue" type="text" size="25" maxlength="25" border="0">
</form>

[Fang]

<input onblur="document.getElementById('subtotalvalue').value = this.value;" name="textfield4" id="totalvalue" type="text" size="25" maxlength="25" border="0">&nbsp;