如下：

  onLoad: function (options) {
        this.initValidate()
        this.initValidate2()
    },

 // 表单提交时的验证 : 账号登录方式
    initValidate() {
        let rules = {
            username: {
                required: true,
            },
            password: {
                required: true,
            },
            captchaimg: {
                required: true,
                minlength: 4
            },
        }
        let messages = {
            username: {
                required: '请输入用户名',
            },
            password: {
                required: '请输入密码',
            },
            captchaimg: {
                required: '请输入验证码',
                minlength: '请输入4位的验证码',
            },
        }
        console.info(rules)
        this.wxValidate = new wx.wxValidate(rules, messages)
    },
    // 表单提交时的验证 : 手机号登录方式
    initValidate2() {
        let rules = {
            mobile: {
                required: true,
                mobile: true
            },
            captcha: {
                required: true,
                minlength: 4
            },
        }
        let messages =  {
            mobile: {
                required: '请输入手机号码',
                mobile: '手机号码格式不正确'
            },
            captcha: {
                required: '请输入验证码',
                minlength: '请输入4位的验证码',
            },
        }
        this.wxValidate2 = new wx.wxValidate(rules, messages)
    },

提交表单方法中用法：

  if (!this.wxValidate1.checkForm(e.detail.value)) {
            const error = this.wxValidate2.errorList[0]
            wx.vantNotify({
                type: 'warning',
                message: error.msg
            })
            return false
        }
  if (!this.wxValidate2.checkForm(e.detail.value)) {
            const error = this.wxValidate2.errorList[0]
            wx.vantNotify({
                type: 'warning',
                message: error.msg
            })
            return false
        }