Question

I read this code on HTMLCodeTutorial.com:

<FORM>
<TABLE BORDER CELLPADDING=3>
<TR>
<TD><NOBR>radius: <INPUT NAME="Circle_radius" SIZE=4></NOBR></TD>
<TD><INPUT TYPE=BUTTON OnClick="Circle_calc(this.form);" VALUE="calculate"></TD>
<TD ALIGN=RIGHT BGCOLOR="#AACCFF">
<NOBR>circumference: <INPUT NAME="Circle_circumference" SIZE=9></NOBR><BR>
<NOBR>area: <INPUT NAME="Circle_area" SIZE=9></NOBR></TD>
</TR>
</TABLE>
</FORM>

I can’t understand OnClick="Circle_calc(this.form);"

Circle_calc(this.form) isn’t defined anywhere. How does this function work? Is it a built-in function in HTML?

Answer 1

It’s not built-in. If you look at the source code, it’s defined as:

<SCRIPT TYPE="text/javascript">
<!--
function Circle_calc(GeoForm)
{
var CircleRadius = GeoForm.Circle_radius.value;
if (CircleRadius >= 0)
   {
   GeoForm.Circle_circumference.value =  2 * Math.PI * CircleRadius ;
   GeoForm.Circle_area.value =  Math.PI * Math.pow(CircleRadius, 2) ;
   }
else
   {
   GeoForm.Circle_circumference.value =  "";
   GeoForm.Circle_area.value =  "";
   }
}
//-->
</SCRIPT>