JamesTheHacker

node promisify.js
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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

[  
   "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

JamesTheHacker

// Change the tweet on our clone
shallowClone.tweets[3].tweet = 'Hijacking your tweets bruh!';

// Changed :)
console.log(shallowClone.tweets[3]);

// Noooooo! Also change!
console.log(state.tweets[3]);

// Both properties reference the same object

JamesTheHacker

// Deep clone an object
const deepClone = JSON.parse(JSON.stringify(state));

deepClone.tweets[3].tweet = 'Hijacking your tweets bruh!';

// Origional tweet is unchanged
console.log(state.tweets[3].tweet);

// Cloned tweet is changed
console.log(deepClone.tweets[3].tweet);

JamesTheHacker

const deepFreeze = o => Object
  .getOwnPropertyNames(o)
  .forEach(n=> {
    if (typeof o[n] == 'object' && o[n] !== null)
      deepFreeze(o[n]);
    return Object.freeze(o);
  });

JamesTheHacker

// Shallow freeze
Object.freeze(state);

// This will not work
state.twitter = '@zuck';

// Look, it's still @JamesJefferyUK
console.log(state.twitter);

// But this works because we're modifying a reference value (an object)