How to fix 'undefined is not an object' error in react native

I am attempting to move my react-native app code to be in a more structured manner. Originally, I had all of my firebase functions inside the file where I used them, but now I would like to use them in multiple places, so I created a Database.js file with a Database class and all of the functions. For some reason though, whenever I try to use one of the functions from the new class, I get the error "undefined is not an object (evaluating 'this.codesRef.once')" Please help!

So far, I have tried using arrow functions, a constructor, and importing firebase in different ways, all to no avail. I am pretty much stumped on this one.

Have a look at the code... (/project/src/components/forms/KeyForm.js)

import React from 'react';
import { StyleSheet, View, TextInput } from 'react-native';

import db from '../Database.js';

class LoginForm extends React.Component {
  constructor(props) {
    super(props);
  }

  render() {
    return (
      <View style={styles.container}>
        <TextInput
          placeholder="Access Code"
          returnKeyType="go"
          onSubmitEditing={text => {db.checkCode(text.nativeEvent.text)}}
        />
      </View>
    );
  }
}

const styles = StyleSheet.create({ // stylesheet
  // yay styles :)
});

export default LoginForm;

(/project/src/components/Database.js)

//import * as firebase from "firebase";
var firebase = require('firebase');

if (!firebase.apps.length) {
    firebase.initializeApp({
        apiKey: "key",
        authDomain: "domain",
        databaseURL: "url",
        storageBucket: "bucket",
    });
}

class Database {

    codesRef = firebase.database().ref('codes');

    static checkCode(text) {
        let codeIsFound = false;
        this.codesRef.once('value', (db_snapshot) => { // this won't work
          db_snapshot.forEach((code_snapshot) => {
            if (text == code_snapshot.val().value) {
              codeIsFound = true;
              identifier = code_snapshot.key;
            }
          });
        });
        if (codeIsFound) {
            //this.deleteCode(identifier);
            console.log("code found");
            this.props.navigation.navigate('Create'); // side-question => how can i get this working in Database.js? Do i need to use withNavigation?
          } else {
            console.log("code not found");
            );
          }
    };
}

module.exports = Database;

Just to clarify, everything worked 100% fine until i tried to migrate the functions to the Database.js file. Any help is greatly appreciated!