1 <!DOCTYPE HTML> 2 <html> 3 <head> 4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 5 <title>无标题文档</title> 6 </head> 7 8 <body> 9 <script> 10 //真 假 11 var n; 12 alert(typeof(n)) 13 if(n){ 14 alert('真的') 15 }else{ 16 alert('假的') 17 } 18 </script> 19 </body> 20 </html>