javascript - How to add in data before a link from input box -

if see below, code allows users input field ip address , allows them remote in. have altered after ip adds information link after need include http:/ before auto matically have include in input box dont want:

<p>please fill in box ip address:  <input type="text" name="prog_site" id="prog_site" value="http://" /> <a href="http://"     onclick="this.href=(document.getelementbyid('prog_site').value +                        '/web/entry/en/websys/atremote/atremotesetupget.cgi')"     target="_blank">let's go!</a></p> 

i have altered folowing closer?

<p>please fill in box ip address:  <input type="text" name="prog_site" id="prog_site" value="http://" /> <a href="http://"     onclick=".value + 'http:// ',this.href=(document.getelementbyid('prog_site').value +                        '/web/entry/en/websys/atremote/atremotesetupget.cgi')"     target="_blank">let's go!</a></p> 

ok, think i've gotten work fixing typos here , there:

<p>please fill in box ip address:      <input type="text" name="prog_site" id="prog_site" value="" />     <a href="#"        onclick="this.href = ('http://' + document.getelementbyid('prog_site').value + '/web/entry/en/websys/atremote/atremotesetupget.cgi')"        target="_blank">let's go!</a> </p> 

a fiddle testing: http://jsfiddle.net/mc4vt/1/