console 命令行工具 X clear
console
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title></title>
  </head>
  <body>
    <script>
      var str ="Rome was not built in a day";     //字符串
      arr =str.replace(/\s/g);               //去掉所有的空格
      var sum =0;                            //定义一个总和
      for(var i of str)
      {
        sum++;
      }                                     //利用for循环统计字符串的字符个数
      document.write(sum);                  //输出字符串中字符的个数
      
    </script>
  </body>