mutating_demo.js

// Mutating data

const favoriteNumbers = [1,2,3];

// favoriteNumbers.push(4); // Mutated favoriteNumbers

const newFavoriteNumbers = [...favoriteNumbers, 4]; // No mutation here!

const removedOne = favoriteNumbers.slice(1, 2); // Mutates the array, no good

console.log('removedOne', removedOne)

console.log('favoriteNumbers', favoriteNumbers);

let a = 10;

// a = 20; // Mutate `a`
// count++; // Mutated count

const b = a + 10; // NOT mutating a

// console.log(a);
// console.log(b);