Winston: TypeError: logger.child is not a function

Please tell us about your environment:

• _winston version?_
  
  
  
  • [ ] winston@2
  
  
  • [x] winston@3
  
  
• _node -v outputs: v10.15.0
• _Operating System? macOS
• _Language? ES5/6

What is the problem?

const winston = require('winston');

const logger = winston.createLogger({
  transports: [new winston.transports.Console()],
});
logger.info('logger ok.');

const childLogger = logger.child({ test: 'test value' });
childLogger.info('child logger ok');

What do you expect to happen instead?

{"message":"logger ok.","level":"info"}
{"message":"child logger ok.","level":"info"}

Other information

TypeError: logger.child is not a function
    at Object.<anonymous> (/Users/onlybalance/test/logger.js:12:28)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
    at startup (internal/bootstrap/node.js:283:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:743:3)