node.js waits until MySQL is up before init connection, promise based

mysql-check.js

const promise = require('bluebird');
const net = require('net');
const config = require('someConfigTool');

//  ---------------------------------
//  most probably MySQL server will start together with ours(this one)
//  so we have to wait until it up
let tryOnce_ = (opts) => {
  return new promise((resolve, reject) => {
    let client = new net.Socket();
    client.connect(opts, () => {});

    client.on('data', function(data) {
      client.destroy();
      resolve(true);
    });

    client.on('error', function(err) {
      client.destroy();
      reject(err);
    });
  })
};

let try2Connect_ = ( opts, count ) => {
  console.log( 'Connection attempt' );
  return tryOnce_( opts )
    .catch( function( err ) {
      return promise.delay(1000/*assuming 1 sec, could be parameter*/)
        .then( function() {
          return --count ? try2Connect_( opts, count ) : promise.reject( err )
        });
    });
};

let DB_ = false;

let initDB_ = () => {
  return DB_ ?
    promise.resolve() :
    try2Connect_({
        host: config.db.host,
        port: config.db.port  //  i.e. 3306
      }, 30/*attempts number*/ )
      .then( data => {
        console.log( 'MySQL is up.' );
        DB_ = new whateverToInitDB({ /**/ })
      })
      .catch( err => {
        console.log('MySQL server does not response: ' + err.toString() );
        throw err;
      });
};