changing value of a hidden field

[lindajames]

i have a login form that has two textbox fields.

first field is called user
and second field is called password

and i also have a hidden field called host

i want the value of the hidden field "host" to change depending on what is entered as the value for "user".

the "user" field is where a user must enter a full email address and based on this i want to set the value of host field to "mail.domain.com"

so for example, if i typed my email address as [e-mail] in the user field, then just before i click on login it should set the value of the hidden field "host" to mail.yahoo.com

can anyone please tell me how i can do this, and it needs to be compatible with as many browsers as possible.

[RonPK]

Easy one ;). On submitting the form, call a function that sets the value of the "host" field to a substring of the value of the "user" field preceeded by 'mail.'.

<script type="text/javascript"> 
function myfunction(f) { 
  var u = f.user.value; 
  f.host.value = 'mail.' + u.substr(u.indexOf('@')+1); 
} 
</script> 
  
<form action="..." onsubmit="myfunction(this)"> 
...

[Bernard Marx]

Nowt wrong with that at all, but I want to exercise my weakling RegExp muscles,
so I'll just briefly mention:

f.host.value = f.user.value.replace(/.*@/,"mail.");

[lindajames]

Thanks RonPK, that script did perfectly, it works like clockwork

[atteso]

I have a very close problem:

How do I do if I want the hidden field (in this case: host) to get exactly the same value as entered in user field?