源代码
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>享学课堂</title> </head> <body> <p>没有值的变量和数据类型的值都是 <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