JavaScript String 检测字母出现个数

<script>
var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZvshjkdjlksdhbasndhbawnieoqawinsbdvhzohcvikzbncxiouj";
var index=0,count=0,position=0;
index = txt.indexOf("h",position);
document.getElementById("demo").innerHTML=index;
while(index!=-1){
        count++;
           position = index + 1;
        index = txt.indexOf("h",position);
}
document.getElementById("demo").innerHTML=count;
</script>