Used when using purely numerical verification codes, they are organized as follows:
$('#mobile-vcode').unbind( );
$("#mobile-vcode").bind("keyup change",function () {
$(this).val($(this).val().replace(/D/ g,''));
if($(this).val().length==4){
/*ajax checks whether the verification code is correct, and activates the button if it is correct*/
}
});
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
