量角器：TypeError：fn不是函数

Question

运行UI测试时遇到以下错误。我是Javascript的新手所以我一直都在关注示例代码而且我不确定我哪里出错了。有人可以解释为什么我会收到此错误以及适当的解决方案是什么？

错误：

[13:00:19] E/launcher - fn is not a function
[13:00:19] E/launcher - TypeError: fn is not a function

主页对象：

Homepage.prototype = Object.create({}, {
    checkInBtn: {
        get: function () {
            return element(by.css('div.checkin.booking-date input'));
        }
    }, datePickerDay: {
        value: function (day) {
            return element(by.cssContainingText('.ui-datepicker-calendar a', day));
        }
    }, selectCheckInDate: {
        value: function (day) {
            return this.checkInBtn.click().then(this.datePickerDay(day).click());
        }
    },
});
module.exports = Homepage;

Cucumber-Protractor Stepfile

this.When(/^I enter the trip information and search$/, function (table) {
var page = new homepage();
        var checkOutDay = new Date(data["DepartureDate"]).getDate();
        page.selectCheckInDate(checkInDay);
        expect(page.checkInBtn.getText()).to.eventually.have.string(checkInDay);
        });

Answer 1

问题在于selectedCheckInDate

Homepage.prototype = Object.create({}, {
    checkInBtn: {
        get: function() {
            return element(by.css('div.checkin.booking-date input'));
        }
    },
    datePickerDay: {
        value: function(day) {
            return element(by.cssContainingText('.ui-datepicker-calendar a', day));
        }
    },
    selectCheckInDate: {
        value: function(day) {
            var self = this;
            this.checkInBtn.click().then(function() {
                self.datePickerDay(day).click();
            });
        }
    }
});
module.exports = Homepage;