问使用javascript验证表单的正确方法(简单)

EN

function validateRegistrationForm(firstName, lastName, username, password, passwordConfirmation) {
alert("validate form function has been called");
//alert("function has been called");

//---


var firstName = firstName;
//alert(firstName);
var lastName = lastName;
//alert(lastName);
var username = username;
//alert(username);
var password = password;
//alert(password);
var passwordConfirmation = passwordConfirmation;
//alert(passwordConfirmation);

//---

//**The code that I have sectioned off here, I am unsure whether I need it or not, could someone please explain to me why I would do this, and not just reference the parameters in the function directly?**

// Check here if all the fields in the registeration form have been filled.

if ( firstname == null || firstname == "" ) {
    //firstname hasn't been filled out
}

if ( lastName == null || lastName == "" ) {
    //lastname hasn't been filled out
}

if ( username == null || username == "" ) {
    //username hasn't been filled out
}

if ( password == null || password == "" ) {
    //password hasn't been filled out
}

if ( passwordConfirmation == null || passwordConfirmation == "" ) {
    //passwordconfirmation hasn't been filled out
}
}

function generateError(messageText, elementIdentifier) {
alert("error generator called");    
//var element = document.getElementById(elementID);
//var error = document.createTextNode(message);
//element.innerHTML = message;
alert("Element: " + elementIdentifier + ", Reason: " + messageText);
}

function validatePassword(password, passwordConfirmation) {
alert("password check called");
if (password == passwordConfirmation) {
    if (password.length < 8) {
        //password too short
        //alert("password\'s match but they are too short");

        return false;
    } else {
        //passwords match and the right length
        //alert("password\'s match and they are 8 characters or longer");
        return true;
    }
} else {
    //the two do not match
    //alert("they don\'t match")
    generateError("Passwords don\'t match", "password");
    return false;
}
}