I'am using `select_tag` and I want to pass selected value in href `:onchange`

I couldnt fetch the selected value

Please guide me how to fetch the selected value and pass in href

I'am using following code

```
<%= select_tag "name", 
   options_for_select(@user.names.map {|c| [c.firstname,c.id]}),
   :onchange =>"document.location.href='/names/value'" %>

```

In the code in `href='/names/**value**` at the place of **value** I have to pass **selected value**

Thanks