# Exercise: Road-Trip Playlist

Finish five functions that keep a road-trip playlist up to date, adding and removing songs, totaling the play time and checking for a song, and let the tests check each one.

Apprentice · JavaScript · Updated October 30, 2026

Four friends are driving six hours to the lake, and the playlist won't sit still. Someone adds a song at every gas stop, the driver wants one moved to the front, a song that everyone's sick of has to go, and somebody keeps asking "how long is all this, anyway?". You'll write the code behind a small playlist app: five functions in `playlist.js`, each one using what this chapter taught. Tests tell you when each function works.

## Get the exercise code

In the **Exercise** box beside the lesson, choose **Get the starter on GitHub** to open its GitHub repository. Click **Code**, then **Download ZIP**, and unzip it into the folder where you keep this course's work. Or clone it with Git.

The folder holds:

- `playlist.js`: your code. The five functions are already there, each returning a placeholder.
- `trip.js`: a small program that plans a trip with your functions and prints the result. You don't need to change it.
- `playlist.test.js`: the tests that check your functions. You don't need to change these.
- `package.json`: tells Node that the files use `import` and `export`.

Open the folder in VS Code, and open a terminal there with **Terminal > New Terminal**.

## What to do

Every function is already declared, with its parameters, and returns a placeholder for now. The comment above it says what it should do, with examples:

```javascript
/*
 * Add the song to the END of the playlist, then return the playlist.
 *
 * addSong(['Highway Sunrise'], 'Desert Radio') -> ['Highway Sunrise', 'Desert Radio']
 * addSong([], 'Windows Down') -> ['Windows Down']
 */
export function addSong(playlist, title) {
  return playlist;
}
```

The word `export` in front of each function lets the tests and `trip.js` use it. Module 3 explains it properly, in *Modules: import and export*.

1. **Finish `addSong` and `playNext`.** One adds a song to the end of the playlist, the other to the front, so it plays next. Both return the same playlist they were given.
2. **Finish `isOnPlaylist`.** It gives back `true` or `false`. Titles match exactly, capital letters included.
3. **Finish `totalPlayTime`.** It gets an array of song lengths in seconds, such as `[214, 187, 243]`, and gives back their total. Use a loop.
4. **Finish `removeSong`.** It removes the first song with that title. If the song isn't on the playlist, nothing changes.

## Check your work

Run the tests from the exercise folder:

```bash
node --test
```

At first every test fails. That's expected: each function you finish turns its tests green. When a test fails, its message says which songs it used and what it expected, for example *Removing Gas Station Coffee should leave the other three songs, in order.*

To see your functions at work, run the trip planner:

```bash
node trip.js
```

## Hints

- **Work out an example by hand first.** Write down `['Highway Sunrise', 'Desert Radio']` and what it should look like after each function.
- **Ends of the list.** Adding at the end and adding at the front each take one array method. *Adding and Removing Items* has both pairs.
- **Removing takes two steps.** First find where the song is, then remove the item at that place. *Finding Things in an Array* shows how the two methods fit together.
- **The song that isn't there.** Try removing a title that isn't on the list. What does your first step give back, and what does your second step do with it?
- **The running total.** *Looping Through an Array* shows the shape: a variable that starts at 0 before the loop, and grows inside it.

## When you're done

Every test is green, and `node trip.js` prints:

```text
Road-trip playlist:
  1. Sunset Detour
  2. Highway Sunrise
  3. Desert Radio
  4. Windows Down
  5. Mile Marker 9
Desert Radio on the list: true
Total play time: 1147 seconds (19 min 7 s)
```

Now look back at `removeSong`. If a song were on the list three times, how would you change it to remove every copy?

## So what

Adding, removing, totaling and checking: those four jobs are most of what any app does with a list, from a music player's queue to a store's shopping cart. Now you can write all four.

## Key terms

- [push()](https://www.ask-codey.com/glossary/push)
- [unshift()](https://www.ask-codey.com/glossary/unshift)
- [splice()](https://www.ask-codey.com/glossary/splice)
- [includes()](https://www.ask-codey.com/glossary/includes)
- indexOf()
- [for...of Loop](https://www.ask-codey.com/glossary/for-of-loop)

## Related

- [What Is an Array](https://www.ask-codey.com/lessons/javascript-arrays-what-is-an-array)
- [Adding and Removing Items](https://www.ask-codey.com/lessons/javascript-arrays-adding-and-removing)
- [Looping Through an Array](https://www.ask-codey.com/lessons/javascript-arrays-looping)
- [Finding Things in an Array](https://www.ask-codey.com/lessons/javascript-arrays-finding-items)

Source: https://www.ask-codey.com/lessons/exercise-javascript-road-trip-playlist