无法使用 redux-saga 从服务器产生 json 响应 [英] Can't yield json response from server with redux-saga

问题描述

我正在尝试使用堆栈 react redux 和 redux-saga 并了解所需的最少管道.

i am trying to use the stack react redux and redux-saga and understand the minimal needed plumbing.

我做了一个 github repo 来重现我得到的错误:

i did a github repo to reproduce the error that i got :

1. https://github.com/kasra0/react-redux-saga-test.git
2. 运行应用程序:npm run app
3. url : http://localhost:3000/

该应用程序由一个简单的组合框和一个按钮组成.从组合中选择一个值后，单击按钮会发送一个操作，该操作仅包含获取一些 json 数据.服务器收到正确的请求(基于选定的值)，但在 let json = yield call([res, 'json']) 行.我收到错误:

the app consists of a simple combo box and a button. Once selecting a value from the combo, clicking the button dispatch an action that consists simply of fetching some json data . The server recieves the right request (based on the selected value) but at the line let json = yield call([res, 'json']). i got the error :

我从浏览器收到的错误消息:

the error message that i got from the browser :

 index.js:2177 uncaught at equipments at equipments 
   at takeEvery 
   at _callee 
 SyntaxError: Unexpected end of input
 at runCallEffect (http://localhost:3000/static/js/bundle.js:59337:19)
 at runEffect (http://localhost:3000/static/js/bundle.js:59259:648)
 at next (http://localhost:3000/static/js/bundle.js:59139:9)
 at currCb (http://localhost:3000/static/js/bundle.js:59212:7)
 at <anonymous>

它来自我的一个传奇:

import {call,takeEvery,apply,take}  from 'redux-saga/effects'
import action_types                 from '../redux/actions/action_types'

let process_equipments = function* (...args){
    let {department} = args[0] 
    let fetch_url = `http://localhost:3001/equipments/${department}`
    console.log('fetch url : ',fetch_url)
    let res  =  yield call(fetch,fetch_url, {mode: 'no-cors'})
    let json =  yield call([res, 'json']) 
    // -> this is the line where something wrong happens
}

export function* equipments(){ 
    yield takeEvery(action_types.EQUIPMENTS,process_equipments)
}

我在管道中做错了什么，但我找不到在哪里.

I did something wrong in the plumbing but i can't find where.

非常感谢您的帮助！

卡斯拉

推荐答案

从 redux-saga 的观点来看，所有代码都稍微正确——两个 promise 通过 call 顺序执行影响.

From redux-saga viewpoint all code is slightly correct - two promises are been executed sequentially by call effect.

let res  =  yield call(fetch,fetch_url, {mode: 'no-cors'})
let json =  yield call([res, 'json']) 

但是在 no-cors 模式下使用 fetch 意味着响应正文将无法从程序代码中获得，因为请求模式是 opaque这样:https://fetch.spec.whatwg.org/#http-fetch

But using fetch in no-cors mode meant than response body will not be available from program code, because request mode is opaque in this way: https://fetch.spec.whatwg.org/#http-fetch

如果您想从不同来源获取信息，请使用 cors 模式和适当的 HTTP 标头，如 Access-Control-Allow-Origin，更多信息请参见此处:https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

If you want to fetch information from different origin, use cors mode with appropriate HTTP header like Access-Control-Allow-Origin, more information see here: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

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