效果图：
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title></title> </head> <body> 只能输入数字： <input id="txt" onkeydown="return myclick(event)" /> </body> <script> function myclick(e){ var key = e.keyCode; console.log(key); if(key>=48&&key<=57){ return true; }else{ return false; } } </script> </html>