用indexof查找一串字符中某个字符出现的次数：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Indexof</title>
</head>
<body>
<button onclick="myFunction()">点我可查看这一串"one,two,three,one,one,two,three"字符中"one"字符出现的次数</button>
<p id="demo"></p>
<script type="text/javascript">
function myFunction(){
var str = "one,two,three,one,one,two,three";
var count=0;
var index=0;
var key="one";
while((index = str.indexOf(key,index))!= -1){
index += key.length;
count = count+1;
}
document.getElementById("demo").innerHTML = count;
}
</script>
</body>
</html>