JS user name and password verification program

This article provides a sample user name and password for this client-side JavaScript user input to improve the user experience Oh, this is what I found on other websites.

function check (form)
{
if (form.ftpuser.value== "")
{
Alert ("Please enter FTP username!");
return false;
}
if (form.ftppass.value== "")
{
Alert ("Please enter FTP password!");
return false;
}
if (form.randnum.value== "")
{
Alert ("Please enter the verification code!");
return false;
}
return true;
}
-->
</script>

HTML code

FTP account <input name= "Ftpuser" type= "text" class= "Formstyle" id= "Ftpuser" size= ""
&nbsp; FTP password <input name= "ftppass" type= "password" class= "Formstyle" id= "Ftppass" size= ""
&nbsp; Verification Code < Input name= "Randnum" type= "text" class= "Formstyle1" id= "Randnum" size= "8" maxlength= "4" >&nbsp; <input name= "Backpage" type= "hidden" value= "/vhost/" Index.net?type=index "><input name=" Submit "type=" Submit "class=" Buttonyinse "value=" Landing "style=" Cursor:hand ";" "