JavaScript - “标识符已被声明”

Question

使用 localStorage 获取注册/登录表单以处理 HTML 时遇到问题。作为我任务的一部分，我不能使用数据库或 php，即使它们更容易。具体来说，问题发生在我的提交功能期间。

返回的语法错误是“标识符 registerUser 已经声明”，并const reponse = processUser (username.value, password.value)在控制台中突出显示。

这是我的 JavaScript 代码：

//setup form
window.addEventListener("DOMContentLoaded", setupForm);

function setupForm() {
    const form = document.getElementById("login");
    form.addEventListener("submit", handleSubmit);
}

//handle Submit
function handleSubmit(event) {
    event.preventDefault();

    const {
        Username,
        Password,
        login_type,
        result
    } = event.target;

    const processUser = login_type.value == "register" ? registerUser : loginUser;
    const response = processUser(username.value, password.value);
    result.innerHTML = response;
}

//register new user
function registerUser(username, password) {
    window.localStorage.setItem("username", username);
    window.localStorage.setItem("password", password);

    return 'New user ${username} now registered!';
}

//login existing user
function loginUser(username, password) {
    const registeredUser = window.localStorage.getItem("username", username);
    const registeredUser = window.localStorage.getItem("password", password);

    const validUser = username == registeredUser;
    const validPassword = password == registeredUser;

    if (validUser && validPassword) {
        return 'User ${username} successfully logged-in!';
    }
    //error form for incorrect username or password
    else if (!validUser) return 'Incorrect username or password';
}

HTML表单：

<fieldset>
    <form id="login" action="submit" method="post">
        <legend><b>Login here!</b></legend><br />
        <div>
            <label for="username">Username:</label>
            <input id="username" type="text" name="username" required />
        </div>
        <div>
            <label for="password">Password:</label>
            <input id="password" type="password" name="Password" required />
        </div>
</fieldset>
<span>
    <input id="login" type="hidden" name="login_type" value="login" checked="checked"></input>
    <!--Hidden for the purposes of my script working-->
    <input type="submit" value="Submit" /><br /><br />
    <output name="result"></output>
    </fieldset>
</span>

任何帮助将不胜感激，因为这非常令人沮丧！