Different behavior between ES6 and ES2016 using babel on cluster.on

Question

I am trying to use cluster to exploit the benefit of having multi-core CPUs. With code:

var cluster = require('cluster');

if (cluster.isMaster) {
    for(var i = 0; i < 2; ++i) {
        cluster.fork();
    }
    cluster.on('exit', function (worker) {
        console.log('Worker ' + worker.process.pid + ' exitted.');
    });
} else {
    console.log('Worker ' + cluster.worker.process.pid);
    process.exit(0);
}

node worked perfectly with output

Worker 14058
Worker 14064
Worker 14058 exitted.
Worker 14064 exitted.

However, when I tried to use import together with babel, I got problems:

import *  as cluster from 'cluster'

if (cluster.isMaster) {
    for(let i = 0; i < 2; ++i) {
        cluster.fork();
    }
    cluster.on('exit', (worker) => console.log('Worker ' + worker.process.pid + ' exitted.'));
} else {
    console.log('Worker ' + cluster.worker.process.pid);
    process.exit(0);
}

the output (after babel) of node is:

2.js:13
    cluster.on('exit', function (worker) {
            ^

TypeError: cluster.on is not a function
    at Object.<anonymous> (2.js:13:13)
    at Module._compile (module.js:556:32)
    at Object.Module._extensions..js (module.js:565:10)
    at Module.load (module.js:473:32)
    at tryModuleLoad (module.js:432:12)
    at Function.Module._load (module.js:424:3)
    at Module.runMain (module.js:590:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:509:3
Worker 14140
Worker 14146

This looks weird. I am using node v6.4.0, with babel 6.11.4 (babel-core 6.13.2), the content of .babelrc is:

{
  "presets": ["es2016", "es2015"]
}

Any ideas what happened?

score 8 · Accepted Answer · edited May 23 '17 at 12:32

Ok, I figured out the reason, ref: Difference between import X and import * as X in node.js (ES6 / Babel)?

The point is change import * as cluster from 'cluster' to import cluster from 'cluster'.

With import * as cluster from 'cluster', everything that is exportable is exported into an object with name cluster, and it has structure:

{ domain: null,
  _events: {},
  _eventsCount: 0,
  _maxListeners: undefined,
  Worker: 
   { [Function: Worker]
     super_: 
      { [Function: EventEmitter]
        EventEmitter: [Circular],
        usingDomains: false,
        defaultMaxListeners: 10,
        init: [Function],
        listenerCount: [Function] } },
  isWorker: false,
  isMaster: true,
  workers: {},
  settings: {},
  schedulingPolicy: 2,
  SCHED_NONE: 1,
  SCHED_RR: 2,
  setupMaster: [Function],
  fork: [Function],
  disconnect: [Function],
  default: 
   EventEmitter {
     domain: null,
     _events: {},
     _eventsCount: 0,
     _maxListeners: undefined,
     Worker: { [Function: Worker] super_: [Object] },
     isWorker: false,
     isMaster: true,
     workers: {},
     settings: {},
     schedulingPolicy: 2,
     SCHED_NONE: 1,
     SCHED_RR: 2,
     setupMaster: [Function],
     fork: [Function],
     disconnect: [Function] } }

On the other hand, when import cluster from 'cluster', the cluster object is the default export:

EventEmitter {
  domain: null,
  _events: {},
  _eventsCount: 0,
  _maxListeners: undefined,
  Worker: 
   { [Function: Worker]
     super_: 
      { [Function: EventEmitter]
        EventEmitter: [Circular],
        usingDomains: false,
        defaultMaxListeners: 10,
        init: [Function],
        listenerCount: [Function] } },
  isWorker: false,
  isMaster: true,
  workers: {},
  settings: {},
  schedulingPolicy: 2,
  SCHED_NONE: 1,
  SCHED_RR: 2,
  setupMaster: [Function],
  fork: [Function],
  disconnect: [Function] }

score 1 · Answer 2 · answered Oct 28 '20 at 17:55

Form me, I imported one by one, by destructuring what i needed from cluster and it worked :

import { fork, on, isMaster } from 'cluster';

then

   if (isMaster) {
      console.log(`Forking ${numWorkers} workers`);
      const workers = [...Array(numWorkers)].map(_ => fork());

      on('online', worker => console.log(`Worker ${worker.process.pid} is online`));
}

Yuvraj · Answer 3 · 2017-03-16T17:11:54.477

0

require('babel-core/register')({
  presets: ['node6']
});

const app = require('./test.js');
app();

Save your code in test.js and see the magic

edited Mar 16 '17 at 17:11

answered Mar 16 '17 at 16:03

Yuvraj

66
2
9

While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value. – morten.c Mar 16 '17 at 18:02

Different behavior between ES6 and ES2016 using babel on cluster.on

3 Answers3