Why are we not using dot(.) operator instead of bracket. Like object[id].prop instead of object[id][prop]

Tell us what’s happening:

  **Your code so far**

// Setup
var collection = {
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: []
},
5439: {
  albumTitle: 'ABBA Gold'
}
};

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

updateRecords(collection, 5439, 'artist', 'ABBA');
  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36.

Challenge: Record Collection

Link to the challenge:

When you use the . notation, you only can match the single property name

myObj.myProp  // Looks for the property named myProp, even if myProp happens to be a variable holding a different name

object.prop is equivalent of object["prop"] and only matches that specific key. With dot-notation you cannot access properties dynamically (at least in JS).

const pet = {
  type: 'cat'
}

const type = 'dog'

pet.type    --> 'cat'
pet['type'] --> 'cat'
pet[type]   --> undefined  // is equivalent to pet.dog or pet['dog']

Further reading: Property accessors - JavaScript | MDN

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