在form表单提交之前执行一些js判断

我刚开的时候，是用onsubmit属性的，如下所示：

index.php:

<h2>用户登录</h2>
    <form method="post" id="userForm" onsubmit="return isRemeber()">
        <div class="form-group">
            <label for="username">用户名:</label>
            <input type="text" class="form-control" id="username" name ="username" placeholder="Enter username">
        </div>
        <div class="form-group">
            <label for="password">密码:</label>
            <input type="password" class="form-control" id="password" name="password" placeholder="Enter password">
        </div>
        <div class="form-check">
            <label class="form-check-label">
                <input class="form-check-input" type="checkbox" id="remember_me"> 记住密码
            </label>
        </div>
        <button type="button" class="btn btn-primary btn-block">提交</button>
    </form>
</div>

<script>
    function isRemeber() {//保存用户密码
        if ( document.getElementById("remember_me").checked) {
            setCookie("rmbUser","true",7);
            setCookie("username",document.getElementById("username").value,7);
            setCookie("password",document.getElementById("password").value,7);
        }
        else {
            setCookie("rmbUser","false",-1);
            setCookie("username","",-1);
            setCookie("password","",-1);
        }
        return false;//这句话很神奇！！！
    }
</script>
           

我原本以为form表单会判断onsubmit的返回值，如果返回false，就不会提交，结果我错了，这个onsubmit函数确实会执行，但是却是在表单提交之后才执行，就算是onsubmit的值为false，form表单也照样会提交。

于是乎我只好换成用button的onclick函数来进行语句的表单的预处理和提交了。

如下所示：

<h2>用户登录</h2>
    <form method="post" id="userForm">
        <div class="form-group">
            <label for="username">用户名:</label>
            <input type="text" class="form-control" id="username" name ="username" placeholder="Enter username">
        </div>
        <div class="form-group">
            <label for="password">密码:</label>
            <input type="password" class="form-control" id="password" name="password" placeholder="Enter password">
        </div>
        <div class="form-check">
            <label class="form-check-label">
                <input class="form-check-input" type="checkbox" id="remember_me"> 记住密码
            </label>
        </div>
        <button type="button" class="btn btn-primary btn-block" onclick="isRemeber()">提交</button>
    </form>
    <script>
    function isRemeber() {//保存用户密码
        if ( document.getElementById("remember_me").checked) {
            setCookie("rmbUser","true",7);
            setCookie("username",document.getElementById("username").value,7);
            setCookie("password",document.getElementById("password").value,7);
        }
        else {
            setCookie("rmbUser","false",-1);
            setCookie("username","",-1);
            setCookie("password","",-1);
        }
        
        if(...){return ;}//这里可以写一句条件控制是否提交当前表单
        var userForm = document.getElementById("userForm");
        userForm.submit();
    }
</script>