JavaScript30/14 - JavaScript References VS Copying/index-START.html at 1411c4a00d04fff24799fc5f6f0764584fe76745 · wesbos/JavaScript30 · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>JS Reference VS Copy</title>
  <link rel="icon" href="https://fav.farm/🔥" />
</head>
<body>

  <script>
    // start with strings, numbers and booleans
    let age = 100;
    let age2=age;
    console.log(age,age2);
    age =200;
    console.log(age,age2);

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

    // and we want to make a copy of it.
    const team =players;
    console.log(team);
    const team2 = players.slice();
    const team3 = [].concat(players);
    const team4 = [...players];
    const team5 = Array.from(players);

    team2[3]='gem';
    team3[2]='hox';
    team4[3]='ha ha ha';


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

    // 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!

    // one way

    // or create a new array and concat the old one in

    // or use the new ES6 Spread

    // 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: 'Wes Bos',
      age: 80
    };


    // const captain = person;
    // captain.age = 99;

    const cap2 = Object.assign({},person);
    cap2.age =99;
    cap2.number = 23;
    cap2['phone'] = 0173473648;
    Object.assign(cap2,{id:1});

    const cap3 = {...person};
    cap3.number = 3792;


    const hlw = {
      name:'dip',
      age:100,
      social:{
        twitter:'@hello',
        facebook:'hello world'
      }
    }
    const hlw2 = Object.assign({},hlw);
    hlw2.id = 123;

    const hlw3 = JSON.parse(JSON.stringify(hlw));
    hlw3.social.insta = 'helloagain';
    const hlw4 = JSON.stringify(hlw); //not a object anymore.its a string

    // and think we make a copy:

    // how do we take a copy instead?

    // We will hopefully soon see the object ...spread

    // 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.

  </script>

</body>
</html>