一道课题求解,该如何处理

一道课题求解源代码函数缺少一部分,使函数查询输入域的每个字符并计算域中出现多少个字母e(提示:函数缺少

一道课题求解
源代码函数缺少一部分,使函数查询输入域的每个字符并计算域中出现多少个字母e(提示:函数缺少的是for 循环)

HTML code
<htmL><html><head><title></title><script type="text/javascript">function countE(form){    var count = 0;    var inputString = form.mainstring.value.toLowerCase();    var msg = "The string has " + count;    msg += " instances of the letter e."    alert(msg);}</script></head><body><form>Enter any stirng:<input type="text" name="mainstring" size="30"><br/><input type="button" value="Conut the Es" onclick="countE(this.form)"></form></body></html></html>


[解决办法]
JScript code
for(var i=0,len=inputString.length;i<len;i++){     if(inputString.charAt(i)=='e') count++;}