last Item in an array subclass (Javascript)

Question

so I am trying to access the last item in the subclass of the array regardless of the size of the array.

All I got so far was undefined.

 var b = [['hello', 'goodbye'], ['hi', 'bye'], ['day', "night"]];

var first = b[0][0];
var last = b[0][b.length-1];

There is no subclass in this question. Do you mean the subarray? — Heretic Monkey, May 25 '17 at 19:37
What do you expect the value of `last` to equal? Your question isn't very clear. — djfdev, May 25 '17 at 19:37
Possible duplicate of [Access / process (nested) objects, arrays or JSON](https://stackoverflow.com/questions/11922383/access-process-nested-objects-arrays-or-json) — Heretic Monkey, May 25 '17 at 19:38
`b[0][b.length-1]` is `b[0][2]`. As there is no element on index `2` in `b[0]` it will return `undefined` only. — Debug Diva, May 26 '17 at 11:11

score 2 · Answer 1 · answered May 25 '17 at 19:37

2

You're getting the length of the first dimension, and using it in the second dimension. You need to get the length of the second dimension:

var last = b[0][b[0].length-1]

answered May 25 '17 at 19:37

Barmar

score 0 · Answer 2 · answered May 25 '17 at 19:37

0

Do you want "night"?

var last = b[b.length-1][b[b.length-1].length-1]

answered May 25 '17 at 19:37

Junius L · Answer 3 · 2017-05-25T19:40:21.623

0

use the .length of the sub array, instead of the parent array. b.length refers to the parent/main array

 var b = [['hello', 'goodbye'], ['hi', 'bye'], ['day', "night"]];

var first = b[0][0];
var last = b[0][b[0].length-1];
console.log(last)

edited May 25 '17 at 19:40

answered May 25 '17 at 19:38

Junius L

score 0 · Answer 4 · answered May 25 '17 at 19:53

you have an array b = [] which has elements, which themselves are arrays b =[[], [], []]

when you do b.length you get the length of the outermost array which in your case is 3, so it basically is doing this

b[0][3-1] => b[0][2] which is undefined

in languages like Java it would have been IndexOutOfBoundException

Therefore you need to change your approach to

b[0][b[0].length -1]

which will give you length of the inner array element, which is 2

b[0][2-1] => b[0][1] => 'goodbye'

4 Answers4