用indexOf查找一串字符中某个字符出现的次数

 1 <!DOCTYPE HTML>
 2 <html>
 3     <head>
 4         <meta charset="utf-8">
 5         <title>black_tea</title>    
 6     </head>
 7     <body>
 8         <button onclick="myFunction()">
 9             点我可查看这一串"fdgdgsdnfegdgffdgsbhmfdnfhperdnfpjpdnfqumvlb"字符中"dnf"字符出现的次数
10         </button>    
11         <p id="demo"></p>
12         <script type="text/javascript">
13            function myFunction(){
14                  var str = "fdgdgsdnfegdgffdgsbhmfdnfhperdnfpjpdnfqumvlb";
15                  var count=0;
16                  var index=0;
17                  var key="start";
18                  while((index = str.indexOf(key,index))!= -1){
19                   index += key.length;
20                   count = count+1;
21                  }
22                  document.getElementById("demo").innerHTML = count;
23             }
24         </script>    
25     </body>
26 </html>