fmpq.com
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Fmpq教程(fmpq.com)</title> </head> <body> <p>变量的值如果不存在则该变量值为 <b>undefined</b>。</p> <p id="demo"></p> <script> var person; document.getElementById("demo").innerHTML = person + "<br>" + typeof person; </script> </body> </html>
运行结果