❗️Spread and Rest

📒 Add the elements of an existing array into a new array

let addToArr = ['Hello', 'World!', 'JavaScript'];
let arr = ['...spread operator', 'and', ...addToArr1, 'rest operator'];

console.log(arr);

📒 Pass elements of an array as arguments to a function

function addThreeNums(x, y, z) {
  console.log(x + y + z);
}

let nums = [0, 1, 2];
addThreeNums(...nums);
let nums_4 = [0, 1, 2, 3];

addThreeNums(...nums_4);

📒 Copy arrays

let arr = [1, 2, 3];
let arr2 = [...arr]; // like arr.slice()

arr2.push(4);
console.log(arr);
console.log(arr2);

📒 Concatenate arrays

let arr1 = [0, 1, 2];
let arr2 = [3, 4, 5];

// arr1.concat(arr2);
arr1 = [...arr1, 'JavaScript', ...arr2];
console.log(arr1);

💡 REST: condense multiple elements into an array

function multiply(multiplier, ...theArgs) {
  return theArgs.map(function (element) {
    return multiplier * element;
  });
}

let arr = multiply(2, 1, 2, 3); 
//multiplier => 2 , ...theArgs => 1, 2, 3
console.log(arr); // [2, 4, 6]