Disabling submit button unless certain elements are in forms

[zggz12]

I currently have a form that I would like to use JavaScript to disable the submit button unless both fields have more than 3 values, and neither have anything except for A-Z, a-z, and 0-9.

I currently have

<form action=submit.php method=POST />
<input type=text name=username />
<br>
<input type=password name=password />
</form>

I am pretty bad with JavaScript but I can understand most html

[holyhttp]

Do you meant the username and password have each at least 3 characters?
Instead of disabling the submit button, why not just prevent the form from being submitted unless all required fields are valid.

HTML:
<form action="submit.php" method="POST" name="loginform" onsubmit="return validateForm()" />
<input type="text" name="username" />
<br>
<input type="password" name="password" />
<br>
<input type="submit" value="login"/>
</form>

JavaScript:

function validateForm(){
var reg=/[a-zA-Z0-9]{3,}/i

if(document.loginform.username.value.search(reg)==-1){
alert('Your username must be at least 3 alphanumeric characters');
document.loginform.username.focus();
return false;
}
else if(document.loginform.password.value.search(reg)==-1){
alert('Your password must be at least 3 alphanumeric characters');
document.loginform.password.focus();
return false;
}

return true;
}

The function above can be optimized but this is a good start.
Notice all attributes values in the HTML are between quotes and the form is given a name and/or an ID.
The first step is getting the habit to write a clean HTML

[zggz12]

Thank you, this is exactly what I was looking for.

[zggz12]

I have one more question,
how would I make it so that a third field (ip2) would work with nothing, or a correctly formatted ip address?