How to focus on the final element in a JavaScript array

Question

How to focus on the final element in a JavaScript array

My function is almost there, but I am facing an issue:

function prevTrack() {
    if (playlist_index == (playlist.length - 0)) {
        playlist_index = -1;
    } else {
        playlist_index--;
    }
    playlist_status.innerHTML = playlist[playlist_index];
    audio.src = dir + playlist[playlist_index] + ext;
    audio.play();
}

I believe the error lies in the line playlist_index = -1;. Could someone please advise me on how to access the last item in the array? So it should be playlist_index = ???;

javascript arrays function audio

Answer 1

Answer №1

My memory is jogged of Python when setting the index to -1 in order to obtain the final element... nevertheless, this approach does not apply to JS. Instead, you must assign the index as playlist.length - 1.

Answer 2

My memory is jogged of Python when setting the index to -1 in order to obtain the final element... nevertheless, this approach does not apply to JS. Instead, you must assign the index as playlist.length - 1.

Answer 3

Answer №2

It's my belief that

playlist_index = playlist.legth - 1

Answer 4

It's my belief that

playlist_index = playlist.legth - 1

Answer 5

Answer №3

If the index is zero, would you like to set playlist_index to the last item in the array? Alternatively, if the index is greater than zero, should it be set to the first item in the array?

let playlist_index = (playlist_index === 0) 
  ? playlist_index = playlist.length - 1 
  : playlist_index--;

or

let playlist_index = (playlist_index === firstValueOfArray) 
  ? playlist_index = playlist.length - 1
  : playlist_index--;

Answer 6

If the index is zero, would you like to set playlist_index to the last item in the array? Alternatively, if the index is greater than zero, should it be set to the first item in the array?

let playlist_index = (playlist_index === 0) 
  ? playlist_index = playlist.length - 1 
  : playlist_index--;

or

let playlist_index = (playlist_index === firstValueOfArray) 
  ? playlist_index = playlist.length - 1
  : playlist_index--;

Answer 7

Answer №4

It seems like you are attempting to create a loop that goes "around the world" while indexing. A simple way to achieve this is by using the modulo % operator.

const array = ['x', 'y', 'z']
for (let i = 0; i < 10; i++) {
  const element = array[i % array.length];
  console.log(element);  
}

Therefore, you can substitute

if (index == (array.length - 0)) {
    index = -1;
} else {
    index--;
}

with

index = (array.length + index - 1) % array.length;

Answer 8

It seems like you are attempting to create a loop that goes "around the world" while indexing. A simple way to achieve this is by using the modulo % operator.

const array = ['x', 'y', 'z']
for (let i = 0; i < 10; i++) {
  const element = array[i % array.length];
  console.log(element);  
}

Therefore, you can substitute

if (index == (array.length - 0)) {
    index = -1;
} else {
    index--;
}

with

index = (array.length + index - 1) % array.length;

How to focus on the final element in a JavaScript array

Answer №1

Answer №2

Answer №3

Answer №4

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