Generic form validation

If number of form fields are unknown or there are many form in your application and you want to validate all of them in a generic way using less code then you can use logic given below.

HTML Form Code:

        <form method="POST" action="loginform.html" onSubmit="return validateLoginForm(this);">
            <tr><td width="25%" align="right">User Name:</td>
            <td align="left"><input id="username" type="text" name="username" value="" size="35"/></td></tr><br>
            <tr><td width="25%" align="right">Password:</td>
            <td align="left"><input id="password" type="password" name="password" value="" size="35"/></td></tr><br>
            <tr>
            <td colspan=2 align="center"><input type="submit" value="Submit" /></td>
            </tr>
        </form>

function validateLoginForm(formObj){
    for (var i=0; i<formObj.elements.length; i++) {
        var element = formObj.elements[i];
        var trimmedvalue = element.value.trim();
        if (trimmedvalue.length == 0 && element.type != 'submit'){
            alert("Please supply a User ID & Password.");
            return false;
        }
    }
}