javascript中alert的最基本使用

<!DOCTYPE html><html>  <head>    <title>jsl.html</title>    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    <meta http-equiv="description" content="this is my page">    <meta http-equiv="content-type" content="text/html; charset=UTF-8">        <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->    <script type="text/javascript">        function test(){        var i = 3;        alert(i);//alert的使用        i = true;        alert(i);    }        </script>  </head>    <body> <!--   <script type = "text/javascript">document.write("Hello World!");</script> <a href = "#" onclick = "alert('HelloWorld')">請單擊</a> -->  <input type = "button" value = "click me" onclick = "test();"/>   </body></html>