fmpq.com
源代码：
点击运行
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Fmpq教程(fmpq.com)</title> </head> <body> <script> var t1=""; var t2; if (t1===undefined){ alert("t1 is undefined"); } if (t2===undefined){ alert("t2 is undefined"); } </script> </body> </html>
运行结果