问题描述

我想从一个函数返回 fetch API 结果.但我得到了未定义，并且该函数没有返回我获取的数据:

I want to return fetch API result from a function. but I get undefined and that function doesn't return me fetched data :

function func() {
    fetch('https://randomuser.me/api/?results=10')
    .then(response => response.json())
    .then(json => (json.results))
}

let users = func()

console.log(users);

推荐答案

Fetch 是异步的并返回一个promise.无法获取 fetch 返回的数据并同步访问.并且它不能返回 users 因为函数需要同步返回但是 users 的数据将不可用.该函数在 Fetch 收到来自 url 的响应之前返回.没关系，这就是一切都完成的方式，而且一切仍然有效.

Fetch is asynchronous and returns a promise. There is no way to take the data returned by fetch and access it synchronously. And it can't return users because the function needs to return synchronously but the data for users won't be available. The function returns before Fetch has a response from the url. That's okay, that's how everything is done and it all still works.

最灵活的处理方式是从函数中返回承诺.然后你可以在 promise 的结果上使用 then() 并在那里做任何你需要做的事情:

The most flexible way to handle this is to just return the promise from the function. Then you can use then() on the result of the promise and do anything you need to do there:

function func(url) {
    return fetch(url)  // return this promise
    .then(response => response.json())
    .then(json => (json.results))
}

func('https://randomuser.me/api/?results=10')
.then(users => console.log(users))  // call `then()` on the returned promise to access users
.catch(err => /* handle errors */)

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