將API node.js后端（firebase）與react.js連接

Question

我無法連接已連接的node.js后端代碼，並且在后端運行時可以正常工作，但是當我嘗試在前端react.js中使用這些功能時，它將無法正常工作。 我收到一個意外的令牌錯誤，我想是因為它獲取了錯誤的數據。

這是我的后端桌面\\ test \\ src \\ users.js：

var express  = require('express');

var app   = express();                             

var Firebase = require('firebase');

var morgan = require('morgan');      

var bodyParser = require('body-parser');    

var Rebase = require('re-base');

app.use(function(req, res, next) { 

res.setHeader("Access-Control-Allow-Origin", "*");

res.header("Access-Control-Allow-Methods", "POST, PUT, OPTIONS, DELETE, GET");

res.header("Access-Control-Max-Age", "3600");

res.header("Access-Control-Allow-Headers", "Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With");

next();

});


Firebase.initializeApp({

apiKey: test.apiKey,

authDomain: test.authDomain,

databaseURL: test.databaseURL,

projectId: test.projectId,

storageBucket: test.storageBucket,

messagingSenderId: test.messagingSenderId,

serviceAccount: './testapp.json', 

});


var db = Firebase.database();

var usersRef = db.ref("Users/");
console.log("reached here.");
 app.get('/api/users', function(req, res) 
 {
     var array = [];
     usersRef.on("value", function(snapshot)
     {
         snapshot.forEach(function(data) 
         {
             var usernames =data.child("username").val();
             var user = { "username": usernames};
             array.push(user);
         });
          res.json(array);
      });
     });
     app.listen(8000);

 console.log("port is 8000");

desktop \\ test \\ src \\ test.js包含我的Firebase信息。 我把X只是為了在這里顯示它。

module.exports = {     
apiKey: "XXXXXXXXXXXXXXXXXXXXXXUrQT8_WyGeZYSkNIA",
authDomain: "authentication-efba4.firebaseapp.com",
databaseURL: "https://authentication-efba4.firebaseio.com",
projectId: "authentication-efba4",
storageBucket: "authentication-efba4.appspot.com",
messagingSenderId: "XXXXX8179075"

 };

這是我的前端桌面\\ test \\ src \\ App.js：

import React, { Component } from 'react';
import './App.css';

class App extends Component {
  state = {users: []}

  componentDidMount() {
    fetch('/users')
      .then(res => res.json())
      .then(users => this.setState({ users }));
  }

  render() {
    return (
      <div className="App">
        <h1>Users</h1>
        {this.state.users.map(user =>
          <div key={user.id}>{user.username}</div>
        )}
     </div>
    );
  }
}

export default App;

它不是從數據庫中獲取數據，當我運行yarn start時，我什至無法編譯它。 我收到此錯誤：

Unhandled Rejection (SyntaxError): Unexpected token < in JSON at position 0
 6 | 
 7 | componentDidMount() {
 8 |   fetch('/users')
 9 |     .then(res => res.json()) <--
10 |     .then(users => this.setState({ users }));
11 | }
12 | 

Answer 1

使用以下功能拍攝數據庫快照

var ref = db.ref("server/saving-data/fireblog/posts");

// Attach an asynchronous callback to read the data at our posts reference
ref.on("value", function(snapshot) {
  console.log(snapshot.val());
}, function (errorObject) {
  console.log("The read failed: " + errorObject.code);
});

參考： https : //firebase.google.com/docs/database/admin/retrieve-data