Last array in JavaScript, why?

Question

I found out that if we do a code to get first and last arrays like this:

function firstLast(array) {
 var first = array[0];
 var last = array[array.length - 1];
return [first, last];
}

It works, I found that solution to get last array in the internet, but I can’t figure out why the - 1 would give the last instead of the first index since the array itself is counting 0, 1, 2, 3... from the lowest to highest. So why is that? The ++ would not work for that? Can someone give me explanation and/or examples please?

Since the indexes are 0 based, the last index is alway 1 less than the length of the array. — Ori Drori
– Ori Drori, Commented Nov 24, 2019 at 15:12
the index you're using is not -1, it's array.length - 1 instead; which should indeed give you the last index — Addis
– Addis, Commented Nov 24, 2019 at 15:13
If you have 5 elements in the array the indexes are 0,1,2,3,4. Now array.length will return 5, so you need to substract 1 to get 4. — Lux
– Lux, Commented Nov 24, 2019 at 15:38

matthewrpacker · Accepted Answer · 2019-11-24 16:00:41Z

2

Here's an example that you can try in the console:

var places = ['first', 'second', 'third']
=> undefined

places[0]
=> "first"

places.length
=> 3

places.indexOf('third')
=> 2

places.length-1
=> 2

places[places.length-1]
=> "third"

answered Nov 24, 2019 at 16:00

matthewrpacker

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Comments

iceWhispers · Accepted Answer · 2019-11-25 16:09:24Z

0

Thanks guys, seems so easy now that it’s explained. But i couldn’t think about that.. all arrays starts as 0 so - 1 in length shall give the last index value, that would not work in php with index starting as 1 right? Thanks everyone

answered Nov 25, 2019 at 16:09

iceWhispers

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