javascript中获取string的长度

<script>
test();
function test()
{
var s = "JavaScript"
var a = 0;
var b = 0;
var c = 0;
var i = 0;
//var e="";
while(i<s.length)
{
var e = s.charAt(i);
if(e == "J")
{a++;}
else if(e == "a")
{b++;}
else if(e == "v")
{c++;}
i++;

}
document.write(s+"中各字符出现的次数如下:")
document.write("<LI>J/"+a);
document.write("<LI>a/"+b);
document.write("<LI>v/"+c);
}