referenceAndCopy.jade

extends base

block vars
  - var title = 'Reference vs Copy - Object && Array'

block styles
  link(rel="stylesheet" type="text/css" href="styles/referenceAndCopy.css")

block body

  h2 Reference vs Copy
  p check console for values

  script(type="text/javascript").
    // start with strings, numbers and booleans
    let age = 100
    let age2 = age
    console.log(age, age2)
    age = 200
    console.log(age, age2)

    let name = 'Jide'
    let name2 = name
    console.log(name, name2)
    name = 'Akinjide'
    console.log(name, name2)

    // Let's say we have an array
    const players = ['Akinjide', 'Sarah', 'Ryan', 'Poppy']

    // and we want to make a copy of it.
    const team = players

    console.log(players, team)
    // You might think we can just do something like this:
    // team[3] = 'Lux'

    // however what happens when we update that array?

    // now here is the problem!

    // oh no - we have edited the original array too!

    // Why? It's because that is an array reference, not an array copy. They both point to the same array!

    // So, how do we fix this? We take a copy instead!
    const team2 = players.slice()

    // one day

    // or create a new array and concat the old one in
    const team3 = [].concat(players)

    // or use the new ES6 Spread
    const team4 = [...players]
    team4[3] = 'heeee hawww'
    console.log(team4)

    const team5 = Array.from(players)

    // now when we update it, the original one isn't changed

    // The same thing goes for objects, let's say we have a person object

    // with Objects
    const person = {
      name: 'Akinjide Bankole',
      age: 80
    }

    // and think we make a copy:
    // const captain = person;
    // captain.number = 99;

    // how do we take a copy instead?
    const cap2 = Object.assign({}, person, { number: 99, age: 21 })
    console.log(cap2)

    // We will hopefully soon see the object ...spread
    // const cap3 = {...person}

    // Things to note - this is only 1 level deep - both for Arrays and Objects. lodash has a cloneDeep method, but you should think twice before using it.

    const akinjide = {
      name: 'Akinjide',
      age: 100,
      social: {
        twitter: '@akinjide',
        facebook: 'bakinjide'
      }
    }

    console.clear()
    console.log(akinjide)

    const dev = Object.assign({}, akinjide)

    // Poorman deep clone
    const dev2 = JSON.parse(JSON.stringify(akinjide))