I have a form text field called "field_0", and javascript code:

<script language="javascript">
function test() {
var a=document.form1.field_0.value;
alert (a);
}
</script>
<form name=form1 ....>
<input type=text name=field_0>
<input type=text name=field_1>
<....onclick='javascript: test();'>
</form>


if I run this, it pops up correct message box with the "field_0" value.

However if I change a little in javascript code:

<script language="javascript">
function test() {
var fd="field_0";
var a=document.form1.fd.value;
alert (a);
}
</script>

this script will no longer work, how can I use variable "fd" in "document.form...."? any idea?

Thanks.

here fd is a variable having value "field_0"

here field_0 is an object inside form1.

so you cant do what you want to do ?
any way why actually you want this to be done ?
you can try alternatives like getElementById();
hope this helps !!!

thanks, that help me.

Another issue:
getElementById() works only in IE, if I try to use Firefox this will not work, how to solve this issue?

> I have a form text field called "field_0", and javascript code:

First of all, your markup is broken. The HTML tag attributes need to be in the form of key-value pairs with the value being enclosed in double quotes.

> However if I change a little in javascript code this script will no longer work

This is because your JS code now looks for an element with the name 'fd' instead of 'field_0'. Try something like document.form1[fd].value.

But the way you are accessing forms is fundamentally broken, read this excellent article on form access.