What do these three dots in React do?

Question

What does the ... do in this React (using JSX) code and what is it called?

Answer 1

The three dots represent the Spread Operator in ES6. It allows us to do quite a few things in Javascript:

1. Concatenate arrays

   var shooterGames = ['Call of Duty', 'Far Cry', 'Resident Evil'];
   var racingGames = ['Need For Speed', 'Gran Turismo', 'Burnout'];
   var games = [...shooterGames, ...racingGames];
   
   console.log(games)  // ['Call of Duty', 'Far Cry', 'Resident Evil',  'Need For Speed', 'Gran Turismo', 'Burnout']
   

2. Destructuring an array

     var shooterGames = ['Call of Duty', 'Far Cry', 'Resident Evil'];
     var [first, ...remaining] = shooterGames;
     console.log(first); //Call of Duty
     console.log(remaining); //['Far Cry', 'Resident Evil']
   

3. Combining two objects

   var myCrush = {
     firstname: 'Selena',
     middlename: 'Marie'
   };
   
   var lastname = 'my last name';
   
   var myWife = {
     ...myCrush,
     lastname
   }
   
   console.log(myWife); // {firstname: 'Selena',
                        //   middlename: 'Marie',
                        //   lastname: 'my last name'}
   

There's another use for the three dots which is known as Rest Parameters and it makes it possible to take all of the arguments to a function in as one array.

4. Function arguments as array

    function fun1(...params) { 
   
    }