在 JSF 中提交表单之前使用 JS 进行客户端验证

我正在尝试对我的注册表进行一些客户端验证。它应该只是停止提交并显示一些文本来帮助用户了解出了什么问题。

这是我的 XHTML：

            <h:form>
                <div class="form-group mx-auto">
                    <h:outputLabel for="emailInput" value="Email"></h:outputLabel>
                    <p:inputText type="text" class="form-control" id="emailInput"   value="#{signupBackingBean.email}" required="true"></p:inputText>
                    <small id="emailError1" class="form-text">Field is required</small>
                    <small id="emailError2" class="form-text">Not avalid emailadress</small>

                </div>
                <div class="form-group mx-auto">
                    <h:outputLabel for="usernameInput" value="Username"></h:outputLabel>
                    <p:inputText type="text" class="form-control" id="usernameInput"  value="#{signupBackingBean.username}" required="true">
                        <f:validateLength minimum="5" maximum="20"></f:validateLength>
                    </p:inputText>
                    <p:message for="@previous" />
                </div>
                <div class="form-group mx-auto">
                    <h:outputLabel for="passwordInput" value="Password"></h:outputLabel>
                    <p:password class="form-control" id="passwordInput"  value="#{signupBackingBean.password}" match="passwordInput2" feedback="true" required="true" inline="true" ></p:password>
                </div>
                <div class="form-group mx-auto">
                    <h:outputLabel for="passwordInput2" value="Password Confirmation"></h:outputLabel>
                    <p:password class="form-control" id="passwordInput2"  value="#{signupBackingBean.password}" required="true"></p:password>
                    <p:message for="@previous" />
                </div>
                <div class="form-group mx-auto">
                    <h:commandButton type="submit" class="btn btn-primary mx-auto btn-block" onclick="return showErrorMessages()"  action="#{signupBackingBean.add}" value="Register" ></h:commandButton>
                </div>
            </h:form>

JS

var email = document.getElementById("emailInput");

function showErrorMessages() {
        document.getElementById("emailError1").style.display = inline;
}

CSS：

#emailError1{
    display: none;
}

计划是触发 Primeface 验证（不能为空）并使描述文本内联。然而，我不确定如何做到这一点。现在我只是试图将它连接到提交命令按钮，但 id 更容易做到更早，这也将起作用。

提前致谢！