FreeCodeCamp question

gistfile1.txt

// Setup
var collection = {
    2548: {
      album: "Slippery When Wet",
      artist: "Bon Jovi",
      tracks: [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    2468: {
      album: "1999",
      artist: "Prince",
      tracks: [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    1245: {
      artist: "Robert Palmer",
      tracks: [ ]
    },
    5439: {
      album: "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function update(id, prop, value) {
  // you could potentially decompose conditional, depending on usage frequency
  // http://refactoring.com/catalog/decomposeConditional.html
  if (prop === "tracks" && value !== "") {
    collection[id][prop].push(value);
  } else if (value !== ""){
    collection[id][prop] = [value];
  } else {
    delete collection[id][prop];
  }

  return collection;
}

// Alter values below to test your code
update(5439, "tracks", "returns error");