Here is a calculator in Java-Script which is a minor modification of a calculator by Axel zur Strassen.
Source:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<TITLE></TITLE>
<SCRIPT language="JavaScript">
<!--
function Ergebnis(FormIndex,ElemIndex)
{
var x = 0;
x = eval(document.forms[FormIndex].elements[ElemIndex].value);
document.forms[FormIndex].elements[ElemIndex].value = x;
}
function Clear(FormIndex,ElemIndex)
{
document.forms[FormIndex].elements[ElemIndex].value = "";
}
function Hinzufuegen(FormIndex,ElemIndex,Zeichen)
{
document.forms[FormIndex].elements[ElemIndex].value =
document.forms[FormIndex].elements[ElemIndex].value + Zeichen;
}
function Sonderfunktion(FormIndex,ElemIndex,Funktion)
{
if(Funktion == "sqrt")
{
var x = 0;
x = eval(document.forms[FormIndex].elements[ElemIndex].value);
document.forms[FormIndex].elements[ElemIndex].value = Math.sqrt(x);
}
if(Funktion == "pow")
{
var x = 0;
x = eval(document.forms[FormIndex].elements[ElemIndex].value);
document.forms[FormIndex].elements[ElemIndex].value = x * x;
}
if(Funktion == "log")
{
var x = 0;
x = eval(document.forms[FormIndex].elements[ElemIndex].value);
document.forms[FormIndex].elements[ElemIndex].value = Math.log(x);
}
}
//-->
</SCRIPT>
</HEAD>
<BODY>
<P><FORM method=post><!-- forms[0] --></P>
<CENTER><TABLE BORDER=1 CELLPADDING=10 BGCOLOR="#808080">
<TR>
<TD bgcolor=#C0C0C0><INPUT size=30 maxlength=30></TD>
</TR>
<TR>
<TD>
<TABLE>
<TR>
<TD width=50><INPUT type=button value=" 7 " onClick="Hinzufuegen(0,0,'7')"></TD>
<TD width=50><INPUT type=button value=" 8 " onClick="Hinzufuegen(0,0,'8')"></TD>
<TD width=70><INPUT type=button value=" 9 " onClick="Hinzufuegen(0,0,'9')"></TD>
<TD width=50><INPUT type=button value=" + " onClick="Hinzufuegen(0,0,'+')"></TD>
</TR>
<TR>
<TD width=50><INPUT type=button value=" 4 " onClick="Hinzufuegen(0,0,'4')"></TD>
<TD width=50><INPUT type=button value=" 5 " onClick="Hinzufuegen(0,0,'5')"></TD>
<TD width=70><INPUT type=button value=" 6 " onClick="Hinzufuegen(0,0,'6')"></TD>
<TD width=50><INPUT type=button value=" - " onClick="Hinzufuegen(0,0,'-')"></TD>
</TR>
<TR>
<TD width=50><INPUT type=button value=" 1 " onClick="Hinzufuegen(0,0,'1')"></TD>
<TD width=50><INPUT type=button value=" 2 " onClick="Hinzufuegen(0,0,'2')"></TD>
<TD width=70><INPUT type=button value=" 3 " onClick="Hinzufuegen(0,0,'3')"></TD>
<TD width=50><INPUT type=button value=" * " onClick="Hinzufuegen(0,0,'*')"></TD>
</TR>
<TR>
<TD width=100 colspan=2>
<INPUT type=button value=" = " onClick="Ergebnis(0,0)"></TD>
<TD width=70><INPUT type=button value=" . " onClick="Hinzufuegen(0,0,'.')"></TD>
<TD width=50><INPUT type=button value=" / " onClick="Hinzufuegen(0,0,'/')"></TD>
</TR>
<TR>
<TD width=50><INPUT type=button value="sqrt "
onClick="Sonderfunktion(0,0,'sqrt')"></TD>
<TD width=50><INPUT type=button value=" pow "
onClick="Sonderfunktion(0,0,'pow')"></TD>
<TD width=70><INPUT type=button value=" log "
onClick="Sonderfunktion(0,0,'log')"></TD>
<TD width=70><INPUT type=button value=" C " onClick="Clear(0,0)"></TD>
</TR>
</TABLE>
</TD>
</TR>
</TABLE></CENTER>
<P></FORM>
<HR WIDTH="100%"></P>
</BODY>
</HTML>