Passing new value into an object

Question

I can't seem to get the syntax correct to add a new "artist" field with value of "ABBA" to album id 5439, I keep getting an error of undefined "artists", which makes sense but no matter which way I right the insert I seem to be getting it wrong.

The code is meant to check if the value isn't tracks and empty, then add the new property variable passed in, with a value from the value variable. I thought with JSON you could add with obj.prop = "value"; But this didnt seem to work

// 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 updateRecords(id, prop, value) {

  if(prop !== "tracks" && value !== null){
    collection.id[prop] = prop[value];
  }


  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

Answer 1

The error you're getting is:

VM5865:33 Uncaught TypeError: Cannot set property 'artist' of undefined

This means collection.id is undefined. This makes sense, because collection has no id property.

You're also setting the wrong value.

Replace:

collection.id[prop] = prop[value];

With:

collection[id][prop] = value;

collection[id] is the collection you need. [prop] is used to target the collection's "artist" property. value is the value you want to store as "artist".

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 updateRecords(id, prop, value) {

  if (prop !== "tracks" && value !== null) {
    collection[id][prop] = value;
  }

  return collection;
}

// Alter values below to test your code
var result = updateRecords(5439, "artist", "ABBA");
console.log(result['5439'])

Answer 2

collection.id[prop] = prop[value];

Collection doesn't have a property called id. The ids are the properties of the collection object directly.

collection[id][prop] = prop[value];