JSON.stringify()

// Save an object
let lunch = {
	sandwich: 'turkey',
	chips: 'Cape Cod',
	drink: 'Pepsi'
};
localStorage.setItem('lunchOrder', JSON.stringify(lunch));

// Save an array
let drinks = ['Pepsi', 'water', 'lemonade'];
localStorage.setItem('drinkOptions', JSON.stringify(drinks));