51help TIY
码：
<!DOCTYPE html> <html> <body> <h1> JavaScript</h1> <p>。</p> <input id="demo" type="text"> <script> function myFunction() { var x=document.getElementById("demo").value; if(x==""||isNaN(x)) { alert("Not Numeric"); } } </script> <button type="button" onclick="myFunction()">点击这里</button> </body> </html>
查看结果: