将 for 循环变成 foreach 循环不起作用

Question

我正在尝试将 for 循环变成 forEach 循环，但它似乎不起作用...

这是我的代码：

const townDataURL = "[some link I probably can't disclose...]"
const towns2get = [
    "Preston",
    "Fish Haven",
    "Soda Springs"
]

fetch(townDataURL)
    .then((response) => {
        return response.json()
    })
    .then((jsonData) => {
        const towns = jsonData["towns"].filter((item) => {
            // for (let i = 0; i<towns2get.length; i++) {
            //     if (item.name == towns2get[i]) {
            //         return item
            //     }
            // }
            return (towns2get.forEach(elem => {
                return ( (item.name == elem) ? (item) : "Hello?" )
            }))
        })
        console.log(towns)
    })

当我有注释代码运行时，它给了我这个：

(3) [{…}, {…}, {…}]
0: {name: "Fish Haven", photo: "fishhaven.jpg", motto: "This is Fish Heaven.", yearFounded: 1864, currentPopulation: 501, …}
1: {name: "Preston", photo: "preston.jpg", motto: "Home of Napoleon Dynamite.", yearFounded: 1866, currentPopulation: 5204, …}
2: {name: "Soda Springs", photo: "sodasprings.jpg", motto: "Historic Oregon Trail Oasis. The Soda is on Us.", yearFounded: 1858, currentPopulation: 2985, …}
length: 3
__proto__: Array(0)

这正是我想要的，但我想简化我的代码...我现在拥有的是：


[]
length: 0
__proto__: Array(0)

我已经进行了一些调试，我知道我的条件语句与三元运算符工作正常，并且它正在返回一个值...但我似乎无法弄清楚为什么它没有返回它回到 filter 方法...

这样不行吗？或者我是否必须以某种方式将 forEach 与 filter 放在一起？

感谢您的帮助！

Answer 1

这里更好的方法是在过滤方法中使用 .includes 函数

const townDataURL = "[some link I probably can't disclose...]"
const towns2get = [
    "Preston",
    "Fish Haven",
    "Soda Springs"
]

fetch(townDataURL)
    .then((response) => {
        return response.json()
    })
    .then((jsonData) => {
        const towns = jsonData["towns"].filter((item) => {
            if(towns2get.includes(item.name) > -1) return true;
            else return false;
        })
        console.log(towns)
    })

Answer 2

Cris G给了我答案：

.forEach() doesn't return anything, so your .filter() callback returns undefined, a falsey value, for each element. Use filter(item => towns2get.includes(item.name)) – Chris G

所以代码应该是：

const townDataURL = "[some link I probably can't disclose...]"
const towns2get = [
    "Preston",
    "Fish Haven",
    "Soda Springs"
]

fetch(townDataURL)
    .then((response) => {
        return response.json()
    })
    .then((jsonData) => {
        const towns = jsonData["towns"].filter(item => towns2get.includes(item.name))
        console.log(towns)
    })

将 for 循环变成 foreach 循环不起作用

Turn a for loop into a foreach loop not working

javascript

arrays

foreach

for-loop

conditional-operator