Fetch request to local file not working

问题

I\'m trying to make a request in a local file, but I don\'t know when I try to do on my computer show me an error. Is possible make a fetch to a file inside your project?

 // Option 1
 componentDidMount() {
     fetch(\'./movies.json\')
     .then(res => res.json())
     .then((data) => {
        console.log(data)
     });
 }

 error: Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0 at App.js: 10 -->  .then(res => res.json())

 // Option 2
 componentDidMount() {
    fetch(\'./movies.json\', {
       headers : { 
         \'Content-Type\': \'application/json\',
         \'Accept\': \'application/json\'
       }
    })
   .then( res => res.json())
   .then((data) => {
        console.log(data);
   });
 }

 error1: GET http://localhost:3000/movies.json 404 (Not Found) at App.js:15 --> fetch(\'./movies.json\', {
 error2: Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0 at App.js: 10 -->  .then(res => res.json())


 // This works
 componentDidMount() {
   fetch(\'https://facebook.github.io/react-native/movies.json\')
   .then( res => res.json() )
   .then( (data) => {
      console.log(data)
   })
 }

回答1:

You are trying to serve a static file with a fetch command, which inherently requires the file to be served by a server. To resolve the issue, you have a few options available to you. I am going to outline the two that are most commonly suggested for such a thing:

• Use Node.js and something like expressjs to host your own server that serves the file you want to fetch. While this procedure might require more effort and time, it is certainly more customizable and a good way to learn and understand how fetching from a backend works.
• Use something like Chrome Web Server to easily set up a very simple server to serve your file on your local network. Using this method, you have very little control over what you can do with said web server, but you can quickly and easily prototype your web application. However, I doubt there's a way to move this method to production.

Finally, there are other options where you can upload one or more files online and fetch them from an external URL, however this might not be the optimal strategy.

回答2:

Your JSON file needs to be served by the server so you need the express server (or any other). In this example we are using using express.

Note: you can also download git repo

App.js File

import React, { Component } from 'react';

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: null
    };
  }

  componentDidMount() {
    const myHeaders = new Headers({
      "Content-Type": "application/json",
      Accept: "application/json"
    });

    fetch("http://localhost:5000/movie", {
      headers: myHeaders,

    })
      .then(response => {
        console.log(response);
        return response.json();
      })
      .then(data => {
        console.log(data);
        this.setState({ data });
      });
  }

  render() {
    return <div className="App">{JSON.stringify(this.state.data)}</div>;
  }
}

export default App;

server.js

var express = require("express");
var data = require('./movie.json'); // your json file path
var app = express();


app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

app.get("/movie", function(req, res, next) {
  res.send(data);
});

app.listen(5000, () => console.log('Example app listening on port 5000!'))

回答3:

Try to place your json file in the public folder like so :

public/movies.json

and then fetch using

fetch('./movies.json')

or

fetch('movies.json')

I have experienced the same problem previously. When I place the json file in the public folder, problem is solved. When using fetch, React normally reads asset/resources files in the public folder.

回答4:

My go-to approach is to use express-generator to set up a quick local server, then run ngrok (free tier is fine) and point your app to the url it creates. This has the advantage of letting you easily test your fetching in the iOS simulator or Android emulator, as well as on a device not tethered to your computer. Plus, you can also send the url to people testing your app. Of course, there would need to be a way for them to manually input that url so the app could set it as the fetch endpoint.

来源：https://stackoverflow.com/questions/50007055/fetch-request-to-local-file-not-working