Record collection question

I’ve been working on this problem for a day and a half now.

My question is:

collection[id][prop]=[value]; // What is this doing?

and why is the above different from:

collection[id][prop] = value;

That is what’s confusing me.


The first one puts the value in an array, the second is not.

So if the value was 1, then the first one is [1], the second one is 1

Thank you Dan. So to further clarify you are saying to put a value where one does not exist in a collection object, the syntax is:

collectionObject[someId][someProp] = [someValue];

What about

collectionObject[someId][someProp] = someValue;

What is the logic to that?

to rephrase…

function updateRecords(id, prop, value) {
  if (prop === "tracks" && value !== "") { // if prop === tracks and value is not empty
   if(collection[id][prop]) { // if id and prop exist
    collection[id][prop].push(value); // push the value (in this case ABBA the artist to the end of the tracks array.
   else {
    collection[id][prop]=[value]; // Other wise???? What is [value] doing, why not just value why the brackets?
  } else if (value !== "") { // if value is not empty (if artist argument is provided when the function is called)
    collection[id][prop] = value; // ??? why is this not in brackets? This is where my confusion is. 
  } else {
    delete collection[id][prop];

  return collection;

tracks is supposed to be array of tracks. [value] isn’t special syntax, it’s just a value in an array, like [1,2,3,4] or ['hello']. Because tracks is an array, if it doesn’t exist on the object you need to create it. Just value doesn’t work, because that’s not an array of things.

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I reread the original problem.

= [values] is creating an empty array before

Ok so [value] is creating a new array but not putting anything in that array, right?

a value is being inserted at this line?
collection[id][prop] = value;

So say you have functions that looks like:

function example1(value) {
  return value;

function example2(value) {
  return [value];

So if I execute example1('hi'), it returns 'hi'. If I execute example2('hi'), it returns ['hi'].

No. As I say this isn’t some special syntax. This is an array with one element, the element is whatever the variable value is:


This is an empty array:


This is an array with five elements in, all with whatever the value of the variable value is:

[value, value, value, value, value]

In the challenge, the property tracks should be an array: it is a list of tracks for a particular album.

If you use the function to add a track to an album, but there is not a tracks property already, then you need to set it to be an array, and to put that track in the array