實例化後返回undefined的屬性值

Question

這是一個使用摩卡來探索TDD的簡單應用程序。該應用程序將獲得兩套撲克牌手並確定獲勝的牌。

我有一些問題，找出爲什麼我的值返回undefined後調用對象上的函數。實例化後，各個變量正確存儲;但使用函數檢索這些較早值的變量將返回它們爲未定義的值。一般來說，我對節點/網絡開發不熟悉，我能想到的唯一可能是sync/async？

的代碼可以在github here

在這裏找到是終端：

images/undefined/undefined.img 
{"suit":9,"val":1,"img":"images/undefined/undefined.img"} 


    Test card module 
    ✓ card is not null 
    ✓ has all arguments valid and present 
    ✓ has image value property 
    1) has valid image path 

    3 passing (13ms) 
    1 failing 

    1) Test card module has valid image path: 
    AssertionError: expected [Function] to equal 'images/s/1.img' 
     at Context.<anonymous> (test/cardTest.js:35:36) 

和下面是測試文件：

'use strict' 

const app = require('express'), 
     mocha = require('mocha'), 
     chai = require('chai') 

let expect = chai.expect 

let card = require('../app/card.js') 

describe('Test card module',() => { 

    const myCard = new card.card('s', 1) 
    console.log(JSON.stringify(myCard)) 

    it('card is not null',() => { 

    expect(myCard).is.not.null 
    }) 

    it('has all arguments valid and present',() => { 

    expect(myCard).has.property('suit') 
    expect(myCard).has.property('val') 
    }) 


    it('has image value property',() => { 

    expect(myCard).has.property('getCardImage') 
    }) 

    it('has valid image path',() => { 

    expect(myCard.getCardImage).to.equal('images/s/1.img') 
    }) 


}) 

和最後應用文件：

'use strict' 

function card(suit, val) { 

    this.suit = suit 
    this.val = val 
    this.img = this.getCardImage() 
} 

card.prototype.getCardImage =() => { 

    console.log('images/' + this.suit + '/' + this.val + '.img') 
    let location = 'images/' + this.suit + '/' + this.val + '.img' 

    return location 
} 

exports.card = card; 

任何解釋將不勝感激;謝謝！

Answer 1

你需要調用函數

expect(myCard.getCardImage()).to.equal('images/s/1.img') 

而且因爲你有動力方面this它

card.prototype.getCardImage = function() { 

    console.log('images/' + this.suit + '/' + this.val + '.img') 
    let location = 'images/' + this.suit + '/' + this.val + '.img' 

    return location 
}