console 命令行工具 X clear
console
<!DOCTYPE html> 
<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    
</head>
<body>
   <script>
       //字符串
       var f_str = "Rome was not built in a day";
       //删除字符串中的空格
       fx_str = f_str.replace(/\s/g,'');
       //用于统计个数
       var num = 0;
       for(var n of f_str){
           ++num;
       }
       document.write("该字符串中字符的个数：" + num + "<br/>");

       document.write("<br/>");

       var num1 = 0;
       for(var n of fx_str){
           ++num1;
       }
       document.write("删除字符串中的空格后，该字符串中字符的个数：" + num1 + "<br/>");


    </script> 
</body>
</html>