const coins = {
  'penny': 1,
  'nickel': 5,
  'dime': 10,
  'quarter': 25
}

const coinsByAmount = Object.keys(coins).reverse();

function getChange(amount) {
  let change = [];

  for(let coinType of coinsByAmount) {
    let coinValue = coins[coinType];

    while(amount >= coinValue) {
      change.push(coinType);
      amount -= coinValue;
    }
  }

  return change;
}