<!DOCTYPE HTML>
<html>
    <head>
        <title></title>
        
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <link rel="stylesheet" href="https://cdn.bootcss.com/twitter-bootstrap/4.3.1/css/bootstrap.min.css">
        <script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.min.js"></script>
        <script src="https://cdn.bootcss.com/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script>
        <style>
        </style>
    </head>
    <body>
    </body>
    <script type="text/javascript">
       var str="Hello world!";
      console.log(str.charAt(0)); //H
    </script>
</html>
Javascript如何获取到字符串的第一位元素_bootstrap