Javascript ascii-mandelbrot set

<html><head><title>Javascript ascii-mandelbrot set</title>
<SCRIPT LANGUAGE="JavaScript">
<!--
function Mandelbrot()
{   var Chars = " .,:;=|iI+hHOE#$-";
    document.writeln("<pre>");
    for(Im=-1.2; Im<=1.2; Im+=.05)
    {   for(Re=-2; Re<=1; Re+=.03)
        {   var Zr = Re;
            var Zi = Im;
            var n = 0;
            for(; n<16; n++)
            {   var Zr2 = Zr*Zr;
                var Zi2 = Zi*Zi;
                if(Zr2+Zi2 > 4) break;
                Zi = 2*Zr*Zi+Im; Zr = Zr2-Zi2+Re;
            }
            document.write(Chars.charAt(n));
        }
        document.writeln("");
    }
    document.writeln("</pre><br>");
    document.close();
}
// -->
</SCRIPT>
</head>
<body>
<H2>Javascript-generated ascii mandelbrot set</H2>
<form name=Frm><input type=button value="Proceed" onClick="Mandelbrot()"><br>
</form></body></html>