mutability2.js

var favoritePlanets = ["Mars", "Saturn", "Earth"];
console.log(favoritePlanets);     // Logs: [ 'Mars', 'Saturn', 'Earth' ]

favoritePlanets.sort();
console.log(favoritePlanets);     // Logs: [ 'Earth', 'Mars', 'Saturn' ]

favoritePlanets.push("Jupiter");  // Logs: 
console.log(favoritePlanets);     // Logs: [ 'Earth', 'Mars', 'Saturn', 'Jupiter' ]

favoritePlanets[0].concat("2");
console.log(favoritePlanets);     // Logs: [ 'Earth', 'Mars', 'Saturn', 'Jupiter' ]

var lifeDiscovered = {
  "Earth": true,
  "Mars": false,
  "Titan": false,
};

console.log(lifeDiscovered);
  // Logs: { Earth: true, Mars: false, Titan: false }

lifeDiscovered["Mars"] = true;
console.log(lifeDiscovered);
  // Logs: { Earth: true, Mars: true, Titan: false }