Top 10 Must‑Know Node.js v6 Features Over v4

Node.js v6 is now LTS, while v7 is current. Let’s look at the features in Node v6 compared to v4 that are worth noting.

1. Integrated Chrome DevTools

Run node --inspect --debug-brk file.js and a debug URL is printed; open it in Chrome to use familiar DevTools for debugging Node code, with live code editing and full asynchronous call stacks.

2. Retrieve all event names from an EventEmitter instance

Calling emitter.eventNames() lists all event names that the emitter is listening to.

const EventEmitter = require('events');
const ee = new EventEmitter();
ee.on('foo', () => {});
ee.on('bar', () => {});
console.log(ee.eventNames()); // ['foo', 'bar']

3. Revised Buffer constructor API

The old new Buffer() constructor is deprecated because its behavior can be error‑prone. Use the clearer APIs: Buffer.from(): creates a Buffer from a string, array, or existing Buffer. Buffer.alloc(): allocates a Buffer of a given size, zero‑filled.

4. Warning for unhandled Promise rejections

In earlier Node versions an unhandled rejection emitted an unhandledRejection event on process. In v6 a warning is shown directly.

$ node
> new Promise((resolve, reject) => { setTimeout(() => { reject(new Error('Whoa!')) }, 100) })
Promise { <pending> }
> (node:35449) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Whoa!

5. Fast and safe creation of temporary directories

Use the native fs.mkdtemp(prefix) method, which appends a 6‑character random string to the prefix.

fs.mkdtemp('/tmp/foo-', (err, folder) => {
  if (err) throw err;
  console.log(folder); // -> /tmp/foo-itXde2
});

6. Preserve symbolic links

This feature affects how require resolves modules. Without preserving symlinks, a module may break because Node resolves the real path.

- app
  - index.js // require('dep1')
  - node_modules
    - dep1 -> ../../mods/dep1
    - dep2 -> ../../mods/dep2
- mods
  - dep1
    - index.js // require('dep2') -> break!
  - dep2
    - index.js

v6 adds the CLI option --preserve-symlinks to change this behavior, but use it cautiously as it can break many modules.

7. New process warning API

You can now listen for process warnings with process.on('warning', (warning) => {}) and emit a warning via process.emitWarning('something'), which is useful for logging.

8. Prevent timing attacks

The new crypto.timingSafeEqual() method helps avoid timing attacks.

9. Directly view V8 performance profiling reports

Run node --prof bench.js to generate a V8 log, then use node --prof-process isolate-0x...-v8.log to obtain a readable report.

10. CPU time

The new process.cpuUsage() interface returns user and system CPU time.

const usage = process.cpuUsage(); // { user: 38579, system: 6986 }