docker-compose: nodejs + mysql can't connect mysql

I try to dockerlized my own node application, but can't connect the mysql container. my codes:

docker-compose.yml

  version: '3.2'
  services:
    node:
      build: ./
      ports:
        - "8787:8787"
      depends_on:
        - db
      networks:
        - docker_xxx
      environment:
        - PORT=8787
        - DATABASE_HOST=db
        - DATABASE_PASSWORD=xxx
        - EGG_SERVER_ENV=local
        - NODE_ENV=development
      # command: ["./wait-for-it.sh", "db:3306", "--", "npm run docker"]
    db:
      build: ./db
      networks:
        - docker_xxx
      environment:
        - MYSQL_ROOT_PASSWORD=xxx
        - MYSQL_DATABASE=database
        - MYSQL_USER=user
        - MYSQL_PASSWORD=passwd

  networks:
    docker_xxx:
      driver: bridge

./Dockerfile (for nodejs)

  FROM node:8.9.4-alpine

  RUN mkdir -p /usr/src/app

  WORKDIR /usr/src/app

  COPY package.json /usr/src/app/

  RUN npm install --production

  COPY . /usr/src/app
  # COPY wait-for-it.sh /usr/src/app

  EXPOSE 8787

  CMD npm run docker

db/Dockerfile (for mysql)

  FROM mysql:5.6

  ADD honggang.sql /docker-entrypoint-initdb.d

config/config.default.js

 config.mysql = {
    // mysql settings
    client: {
      // host
      host: process.env.DATABASE_HOST || '127.0.0.1',
      // port
      port: '3306',
      // username
      user: 'root',
      // password
      password: 'xxx',
      database: 'xxx',
      charset: 'utf8',
      dialectOptions: {
        collate: 'utf8_general_ci',
      },
    },
    app: true,
    agent: false,
  };

I run docker-compose up -d , there's only db running.

I run docker logs hash to find errors, it shows the following info:

        2018-04-30 14:43:51,334 ERROR 54 nodejs.ECONNREFUSEDError: connect ECONNREFUSED 172.19.0.2:3306
            at Object._errnoException (util.js:1022:11)
            at _exceptionWithHostPort (util.js:1044:20)
            at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1182:14)
            --------------------
            at Protocol._enqueue (/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:145:48)
            at Protocol.handshake (/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:52:23)
            at PoolConnection.connect (/usr/src/app/node_modules/mysql/lib/Connection.js:130:18)
            at Pool.getConnection (/usr/src/app/node_modules/mysql/lib/Pool.js:48:16)
            at /usr/src/app/node_modules/ali-rds/node_modules/pify/index.js:29:7
            at new Promise (<anonymous>)
            at Pool.<anonymous> (/usr/src/app/node_modules/ali-rds/node_modules/pify/index.js:12:10)
            at Pool.ret [as getConnection] (/usr/src/app/node_modules/ali-rds/node_modules/pify/index.js:56:34)
            at Pool.query (/usr/src/app/node_modules/mysql/lib/Pool.js:202:8)
            at /usr/src/app/node_modules/ali-rds/node_modules/pify/index.js:29:7
            sql: select now() as currentTime;
        code: 'ECONNREFUSED'
        errno: 'ECONNREFUSED'
        syscall: 'connect'
        address: '172.19.0.2'
        port: 3306
        fatal: true
        name: 'ECONNREFUSEDError'
        pid: 54
        hostname: d9cd95667a5d

I added CMD ping db, it responded.

I tried to use wait-for-it.sh (the code just commented out), but got the error info:

env: can't execute 'bash': No such file or directory