JamesTheHacker

// This function waits for an unknown amount of time
const wait = (delay, callback) => {
  // setInterval returns an ID. We need this to stop the timer
  const id = setInterval(() => {
    // Generate a random number between 0 and 1
    const rand = Math.random();

    if (rand > 0.95) {
      // Call the callback function. Note the first parameter is an error
      callback(null, 'Congratulations, you have finished waiting.');

JamesTheHacker

// Calling wait and passing a callback
wait(1000, (err, data) => {
  // Did the function return an error?
  if (err) throw new Error(err);
  // Output the data
  console.log(data);
});

JamesTheHacker

node promisify.js
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Congratulations, you have finished waiting.

JamesTheHacker

node promisify.js
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Waiting ...
Waiting ...

JamesTheHacker

const util = require('util');

// Here we use util.promisify to convert the function to a promise
const waitAsync = util.promisify(wait);

//And here we use the promisified function. Cool huh?
waitAsync(1000)
  .then(data => console.log(data))
  .catch(err => console.error(`[Error]: ${err}`));

JamesTheHacker

const wait = (delay, callback) => { /* … */ };

JamesTheHacker

const util = require('util');

// This function waits for an unknown amount of time
const wait = (delay, callback) => {
  // setInterval returns an ID. We need this to stop the timer
  const id = setInterval(() => {
    // Generate a random number between 0 and 1
    const rand = Math.random();

    if (rand > 0.95) {

JamesTheHacker

[  
   "nodejs ",
   [  
      [  
         "\u003cb\u003enode js\u003c\/b\u003e \u003cb\u003etutorial\u003c\/b\u003e",
         0,
         [  
            10
         ],
         {  

JamesTheHacker

const state = {
  twitter: '@JamesJefferyUK',
  tweets: [
    {
      tweet: 'I <3 JavaScript',
      read: false
    },
    {
      tweet: 'React is so cooool',
      read: false

JamesTheHacker

// This is how you shallow clone an object
const shallowClone = Object.assign({}, state);

// Change the twitter handle
shallowClone.twitter = '@zuck';

// Origional state isn't changed
console.log(state.twitter); // @JamesJefferyUK

// Changed