导出已在导出函数中使用的变量答案

【问题标题】：Exporting a variable which is already being used inside an exported function导出已在导出函数中使用的变量
【发布时间】：2021-03-25 17:20:14
【问题描述】：

我正在尝试在一个单独的文件中初始化我的 mongodb。我正在函数内部编写初始化并导出函数。现在，我还想导出该函数中写入的数据库。我该怎么做？

我想做这样的事情。

import { MongoClient } from 'mongodb';
import config from '../../config';
import logger from '../../logger';

const connectDB = async () => {
    const client = new MongoClient(config.dbUri, {
        userNewUrlParser: true,
         useUnifiedTopology: true,
    });

    try {
        await client.connect();
        const db = client.db('sample_mflix');
        logger.info('Connected to Database');
    } catch (e) {
        logger.error(e);
    } finally {
        await client.close();
    }
};
export default {
    connectDB,
    db,
};

【问题讨论】：

标签： javascript node.js mongodb ecmascript-6

【解决方案1】：

如果是我，我会避免默认导出并执行以下操作：

import { MongoClient } from 'mongodb';
import config from '../../config';
import logger from '../../logger';

export let db;

export const connectDB = async () => {
    const client = new MongoClient(config.dbUri, {
        userNewUrlParser: true,
         useUnifiedTopology: true,
    });

    try {
        await client.connect();
        db = client.db('sample_mflix');
        logger.info('Connected to Database');
    } catch (e) {
        logger.error(e);
    } finally {
        await client.close();
    }
};

或者如果你想要一个更好的错误

import { MongoClient } from 'mongodb';
import config from '../../config';
import logger from '../../logger';

let db;

export const getDB = () => {
  if (!db) {
    throw new Error("DB Not yet connected");
  }
  return db;
}

export const connectDB = async () => {
    const client = new MongoClient(config.dbUri, {
        userNewUrlParser: true,
         useUnifiedTopology: true,
    });

    try {
        await client.connect();
        db = client.db('sample_mflix');
        logger.info('Connected to Database');
    } catch (e) {
        logger.error(e);
    } finally {
        await client.close();
    }
};

【讨论】：