javascript - 如何按照我需要的顺序获取日志消息？

Question

如何防止首先记录 Service running ... msg？我想要 testDBConnection fn 中的消息。首先被记录。当数据库未运行时，我希望继续记录看起来数据库未运行消息，一旦数据库启动数据库连接已建立和服务正在运行... 消息应遵循。我尝试了多种方法，但无法想出正确的代码。感谢您的帮助。

index.js

import app from './config/express';
import config from './config/config';
import logger from './config/winston';
import { initDbConnection } from './server/db';

app.listen(config.port, () => {
  initDbConnection();
  logger.info(`Service running and listening on port ${config.port}`);
});

db.js

import knex from 'knex';
import config from '../config/config';
import logger from '../config/winston';

const { db } = config;
let pool;

const testDBConnection = (client) => {
  const intervalId = setInterval(async () => {
    try {
      await client.select(1);
      logger.info('DB connection has been established');
      clearInterval(intervalId);
    } catch (error) {
      logger.error('Looks like DB is not running');
    }
  }, 2000);
};

export const initDbConnection = (mock) => {
  if (mock) {
    pool = knex({});
  } else {
    pool = knex({
      client: 'pg',
      version: '7.4.2',
      connection: db,
      debug: true
    });
    testDBConnection(pool);
  }
};

export const getDb = () => pool;

Answer 1

您可以使用 async/await 来实现这一点。

import app from './config/express';
import config from './config/config';
import logger from './config/winston';
import { initDbConnection } from './server/db';

app.listen(config.port, async () => {
  await initDbConnection();
  logger.info(`Service running and listening on port ${config.port}`);
});

db.js:

import knex from 'knex';
import config from '../config/config';
import logger from '../config/winston';

const { db } = config;
let pool, connected;

const testDBConnection = (client) => {
   return new Promise(resolve => {
   const intervalId = setInterval(async () => {
        try {
          await client.select(1);
          if (connected) {
              return;
          }
          connected = true;

          logger.info('DB connection has been established');
          clearInterval(intervalId);
          resolve('success');
        } catch (error) {
          logger.error('Looks like DB is not running');
        }
      }, 2000);
   });
};

export const initDbConnection = (mock) => {
  if (mock) {
    pool = knex({});
  } else {
    pool = knex({
      client: 'pg',
      version: '7.4.2',
      connection: db,
      debug: true
    });
    return testDBConnection(pool);
  }
};

export const getDb = () => pool;

这样，在解析 initDbConnection 之前，不会调用 app.listen cb 内的记录器。另一种方法是只使用 promise then。