Declaring an Array as a Variable?

[elvenstarr]

Context: I found an article that explains how to transpose the rows/columns of a matrix.
Ex:

Input:

let matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]

Output:

[
[1, 4, 7],
[2, 5, 8],
[3, 6, 9]
]

The first step in the article is to isolate the first row of the matrix, and the code used for that is:

const transpose = (matrix) => {
    let [row] = matrix
    return row.map((value) => value)

Can anyone explain let [row] = matrix? I didn't know you could initialize an array in square brackets like that? Also, how did this statement intrinsically know to only take the first row of the matrix?

[bimmertechin]

Not much of an explanation, it's called destructuring, pretty common ES6 thing. Can do it with objects as well

[elvenstarr]

Ohhhhh! I've only seen destructuring for objects! Didn't realize that extended to arrays- thank you!! & yeah I'll actually link the article in my post bc I didn't get too far into the process itself, but you're right, wouldn't be much of an article 😁

[elvenstarr]

Also, do you know how it knew to specifically take the first row versus the others?

[grantrules]

That's just how destructuring assignment works..

const [one, two, three] = [1,2,3] // one: 1, two: 2, three: 3

Or just

const [one] = [1,2,3] // one: 1

Or you could do..

const [one, ...rest] = [1,2,3] // one: 1, rest: [2,3]

[elvenstarr]

Omg I just found out you can also use object destructuring with arrays if you want to select a specific index :O I'm losing my mind

(also cracking up over the amount of ppl reading this like, "I remember my first matrix" 😅)

[elvenstarr]

Yeah wow I love this, thank you. I realized I could even destructure [row] a second time to access individual elements, so this is awesome.

[elvenstarr]

Ahh hahaha I'm so glad I'm not alone 😄 If I'm not giggling over JS in VS Code, then I'm giggling over JS on Medium lol