Lab 8.2

davidmarkclements

that's correct @akudrin 👍

arloi

I'm trying to understand the difference between calling and awaiting a promisified opA(print) vs. print(null, promisified opA) - see code below (comments in the run function):

Can someone help me understand please?

const { promisify } = require('util');
 
const print = (err, contents) => {
  if (err) console.error(err);
  else console.log(contents);
};
 
const opA = (cb) => {
  setTimeout(() => {
    cb(null, 'A');
  }, 500);
};
 
const opB = (cb) => {
  setTimeout(() => {
    cb(null, 'B');
  }, 250);
};
 
const opC = (cb) => {
  setTimeout(() => {
    cb(null, 'C');
  }, 125);
};
 
const promA = promisify(opA);
const promB = promisify(opB);
const promC = promisify(opC);
 
const run = async () => {
  // This does not work, only prints 'A'
  await promA(print);
  await promB(print);
  await promC(print);
 
  // This works as expected
  // print(null, await promA());
  // print(null, await promB());
  // print(null, await promC());
};
 
run().catch(console.error);