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JavaScript Object-Oriented JavaScript (2015) Constructor Functions and Prototypes Playlist Project

Posted by Zak Erving
Zak Erving
22,832 Points

Why does the add method want to take the parameter of 'song'?

At around 3:30 in this video, Andrew says that the add method of Playlist.prototype.add wants to take the parameter 'song', but I have no idea why…'Song' is a constructor function, but that doesn't allow the playlist app to function normally.

Is 'song' just an arbitrary name passed as a parameter because it's the singular state of the 'songs' array?

Zak Erving
Zak Erving
22,832 Points

Also, when do I know that some functions require parameters and others don't?

2 Answers

Kelly von Borstel
Kelly von Borstel
28,880 Points
Kelly von Borstel
Kelly von Borstel
28,880 Points

Inside the Playlist function, on line 2, 'this.songs' is assigned an empty array, []. And then on line 7, a song is 'pushed' to that array. The names 'song' and 'songs' could be anything. For example, you could use 'songName' (instead of song) and 'listOfSongs' (instead of songs). Having the array name be the plural of the individual array element name makes sense in this case, but it's not required.

Kelly von Borstel
Kelly von Borstel
28,880 Points
Kelly von Borstel
Kelly von Borstel
28,880 Points

The song isn't automatically added — it's added using the push method, which is a native array method available to any array. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push

Zak Erving
Zak Erving
22,832 Points

Oh! I see it now! That makes all the sense in the world :) Thank you so much!

Kelly von Borstel
Kelly von Borstel
28,880 Points
Kelly von Borstel
Kelly von Borstel
28,880 Points

Hi, Zak. You're correct, 'song' is just an arbitrary name. You can think of it sort of like a variable name. When the function is called and an argument (some specific song) is passed in, the parameter 'song' takes on that value, which is then pushed to the 'songs' array.

Whether a function needs parameters or not can be confusing. But if you think about what a function is doing, it will help you know what input (parameters) it needs. In this case, the add method is adding a song to an array of songs. Without the song parameter (so that a song can be passed in as an argument), how will the function know what song to add to the array? If that doesn't make sense, let me know, and I'll try to explain it better.

Zak Erving
Zak Erving
22,832 Points

That's very helpful, Kelly. Thank you :)

But how does "song" get automatically added to the "songs" array? Is there some sort of pluralization mechanism in JavaScript that I don't know about?