【JavaScript】填坑，表单提交不执行Ajax方法

一开始我是这么写的

<form id="form0" class="ui large form" action="" method="">
                <div class="ui segment">
                    <div class="field">
                        <div class="ui left icon input">
                            <i class="user secret icon"></i>
                            <input type="text" name="nickName" placeholder="昵称">
                        </div>
                    </div>
                    <div class="field">
                        <div class="ui left icon input">
                            <i class="user icon"></i>
                            <input type="text" name="username" placeholder="用户名">
                        </div>
                    </div>
                    <div class="field">
                        <div class="ui left icon input">
                            <i class="lock icon"></i>
                            <input type="password" name="password" placeholder="密码">
                        </div>
                    </div>
                    <div class="field">
                        <div class="ui left icon input">
                            <i class="lock icon"></i>
                            <input type="password" name="rePassword" placeholder="再次输入密码">
                        </div>
                    </div>
                    <div class="field">
                        <div class="ui left icon input">
                            <i class="lock icon"></i>
                            <input type="email" name="email" placeholder="邮箱">
                        </div>
                    </div>
                </div>
                <div class="ui error message"></div>
                  <button type="button" id="SignUser_btn" class="ui fluid large teal button m-margin-button-mini" >注册</button>
                  <button type="button" id="back_btn" class="ui fluid large teal button" onclick="backHome()">返回</button>
            </form>

<script>
    $('#back_btn').click(function () {
        $.ajax({
            url: '/admin'

        })
    })
    $('#SignUser_btn').click(function () {
        var formData = $('#form0').serialize();
        alert(formData)
        $.ajax({
            type: 'POST',
            url: '/admin/SignUser',
            data: $('#form0').serialize(),
            dataType: 'JSON',
            success:function (data) {
                alert(data)
                alert('success')
            }
        })
    })
</script>

点击注册以后

1.  var formData = $('#form0').serialize();
2.  alert(formData)

这两句也能被执行，搞了好久才发现，不能把按钮写到form表单，不能把按钮写到form表单，不能把按钮写到form表单