How to fix 'Cannot set property 'ref' of undefined'?

Question

So what I try to do is very simple: just receive data from Cloud Firestore.

I have following code:

import React from 'react';
import firebase from "react-native-firebase";

export default class newsFeed extends React.Component {
 constructor() {
  this.ref = firebase.firestore().collection('keys')
}

 async load(id) {
  const doc = await this.ref.doc(id).get()
  if (doc.exists) {
    return doc.data()
  }
 }
}

I receive an error: 'Cannot set property 'ref' of undefined'.

How can I fix it and what's the problem?

Learned it from this tutorial: https://medium.com/react-native-training/firebase-sdk-with-firestore-for-react-native-apps-in-2018-aa89a67d6934

Answer 1

通常箭头功能会有所帮助。

 load = async (id) => { //...

Answer 2

You are exporting the class without creating an instance. You should do something like:

import React from 'react';
import firebase from "react-native-firebase";

class NewsFeed extends React.Component {
 constructor() {
  this.ref = firebase.firestore().collection('keys')
}

 async load(id) {
  const doc = await this.ref.doc(id).get()
  if (doc.exists) {
    return doc.data()
  }
 }
}

export default newsFeed = new NewsFeed();

Hope that helps :)