Which functions could work as synchronous in node.js?

Question

For example, I am writing a random generator with crypto.randomBytes(...) along with another async functions. To avoiding fall in callback hell, I though I could use the sync function of crypto.randomBytes. My doubt is if I do that my node program will stop each time I execute the code?. Then I thought if there are a list of async functions which their time to run is very short, these could work as synchronous function, then developing with this list of functions would be easy.

Answer 1

Using the mz module you can make crypto.randomBytes() return a promise. Using await (available in Node 7.x using the --harmony flag) you can use it like this:

let crypto = require('mz/crypto');

async function x() {
  let bytes = await crypto.randomBytes(4);
  console.log(bytes);
}

x();

The above is nonblocking even though it looks like it's blocking.

For a better demonstration consider this example:

function timeout(time) {
  return new Promise(res => setTimeout(res, time));
}

async function x() {
  for (let i = 0; i < 10; i++) {
    console.log('x', i);
    await timeout(2000);
  }
}

async function y() {
  for (let i = 0; i < 10; i++) {
    console.log('y', i);
    await timeout(3000);
  }
}

x();
y();

And note that those two functions take a lot of time to execute but they don't block each other.

Run it with Node 7.x using:

node --harmony script-name.js

Or with Node 8.x with:

node script-name.js

I show you those examples to demonstrate that it's not a choice of async with callback hell and sync with nice code. You can actually run async code in a very elegant manner using the new async function and await operator available in ES2017 - it's good to read about it because not a lot of people know about those features.

Answer 2

They're asynchronous, learn to deal with it.

Promises now, and in the future ES2017's await and async will make your life a lot easier.

Bluebirds promisifyAll is extremely useful when dealing with any standard Node.js callback API. It adds functions tagged with Async that return a promise instead of requiring a callback.

const Promise = require('bluebird')
const crypto = Promise.promisifyAll(require('crypto'))

function randomString() {
  return crypto.randomBytesAsync(4).then(bytes => {
    console.log('got bytes', bytes)
    return bytes.toString('hex')
  })
}

randomString()
  .then(string => console.log('string is', string))
  .catch(error => console.error(error))