全局访问Node.JS / express中的Firebase

var firebase = require("firebase");
firebase.initializeApp({
  serviceAccount: "../Wrapper-adfd67bc8c36.json",databaseURL: "https://wrapper.firebaseio.com"
});

但是当我尝试在路由文件中访问它时：

var express = require('express');
var router = express.Router();

router.get('/:id',function(req,res,next) {
    functionThatUsesFirebase(req.params.id);

    res.send(req.params.id);
});

我收到错误：

firebase is not defined.

那么我尝试将Firebase添加到路由文件本身：

var express = require('express');
var router = express.Router();
var firebase = require("firebase");
firebase.initializeApp({
  serviceAccount: "../Wrapper-adfd67bc8c36.json",databaseURL: "https://wrapper.firebaseio.com"
});

router.get('/:id',next) {
    functionThatUsesFirebase(req.params.id);

    res.send(req.params.id);
});

我收到控制台错误：

Firebase App named '[DEFAULT]' already exists.

如何让所有路由文件都可以访问Firebase？谢谢！