Question about Record Collection challange from FreeCodeCamp

Why do I have to add square brackets to make this code work? (eg: records[id][prop] = [value]; at below) If I take square brackets away, it cannot fulfill the ” After updateRecords(recordCollection, 5439, “tracks”, “Take a Chance on Me”) , tracks should have the string Take a Chance on Me as the last element.” requirement.

Why?

var recordCollection = {
    2548: {
        albumTitle: 'Slippery When Wet',
        artist: 'Bon Jovi',
        tracks: ['Let It Rock', 'You Give Love a Bad Name']
    },
    2468: {
        albumTitle: '1999',
        artist: 'Prince',
        tracks: ['1999', 'Little Red Corvette']
    },
    1245: {
        artist: 'Robert Palmer',
        tracks: null
    },
    5439: {
        albumTitle: 'ABBA Gold'
    }
};

// Only change code below this line
function updateRecords(records, id, prop, value) {
    if (prop !== 'tracks' && value !== "") {
        records[id][prop] = value;
    } else if (prop === "tracks" && records[id].hasOwnProperty("tracks") === false) {
        records[id][prop] = [value];
    } else if (prop === "tracks" && value !== "") {
        records[id][prop].push(value);
    } else if (value === "") {
        delete records[id][prop];
    }
    return records;
}

updateRecords(recordCollection, 5439, 'artist', 'ABBA');

Answer

tracks props is an array, as defined for Bon Jovi & Prince:
tracks: ["1999", "Little Red Corvette"]

In this statement, you want to add a tracks to the artist:
prop === "tracks".

But the artist hasn’t any tracks yet: records[id].hasOwnProperty(“tracks”) === false.

So you need to init the tracks array before adding any values to it:
records[id][prop] = [value];

---

PS:
You used records[id].hasOwnProperty("tracks") === false. But for Robert Palmer, the props tracks exists and isn’t an array.
You should use :
(records[id].hasOwnProperty("tracks") === false || !Array.isArray(records[id]['tracks])).