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";
            arr = str.replace(/s/g);
            var sum = 0;
            for(var i of str)
            {

                sum++
            }
            document.write(sum);

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