Different use of the equality operators

JavaScript
1

Hi

Having some issues here so hoping someone can shed some light on this for me.

In the part of code : if (prop !== ‘tracks’ && value !== “”),
If I use the (===) here instead of (==) I get a syntax error.

Its fine for the other parts of code but not when I negate the a boolean value (!==), it does not work.

In the piece of code above, I was under the impression that the properties of an object could be written as a string or other as it would be converted to a string and it seemed so in other tasks however, it returns a syntax error here without quotes.

What am I missing here?

I cant use dot notation in this code, anywhere I substitute it I get an error.

And why cant I use undefined instead of empty quotes? Why would there be a set of quotes with nothing for a value as an input where as undefined would work with no input?

Any help is much appreciated. I found this quite hard. I think I need to spend more time to thoroughly understand the material before I move onto another task.

So thanks ahead.

  **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/88.0.4324.182 Safari/537.36 Edg/88.0.705.74.

Challenge: Record Collection

Link to the challenge:

3

Hi Randell
Thanks.

Okay so I have been thinking of the exclamation mark as the negate operator and not in a sequence with the equals operator. So thanks.

5

In the code where tracks is used in the conditional quotes are needed. But in the object collection tracks are not quoted. I didn’t think it mattered if quotes where used or not for an objects property?

7

Right, there is a difference. Here, where the object is being defined:

1245: {
  artist: 'Robert Palmer',
  tracks: []
},

tracks is defining the property. Technically, you could have put it is quotes, but there is no need. For these, quotes are only needed if the property is not a valid JS identifier (contains only alphanum, _, or $ and doesn’t start with a number).

Here:

} else if (prop === "tracks" && !object[id].hasOwnProperty("tracks")) {

They both must be in quotes because they are string literals. prop was passed in as a string so you are checking if it is the string "tracks", and then you are passing a string to the method hasOwnProperty. There is no JS data type of “property”, so we are passing in a string. Inside hasOwnProperty, it will do the proper JS to make the comparison.

This is different than using a property to access a value, where you can use dot notation or bracket notation (bracket notation is necessary if the property name is not a valid JS identifier or if the property name is stored in a variable.)

8

if (prop !== “tracks” && value !== “”)

Tracks here in quotes. I have another reply but will need to study it as I don’t know some of the terms and it take a bit to sink in. Thanks for your help.

9

Right, in that case “tracks” is in quotes because it is a string. The variable props is passed in as a string. There is no data type “property”.

10

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