spread vs slice

spread-vs-slice.md

DON'T DO THIS!

When working on legacy projects it may be tempting to go around changing

const myCopy = arr.slice();

with:

const myCopy = [...arr];

but... DON'T DO IT!

It's not exactly the same.

Example:

const arr = [1,2,3];
arr[10] = 11; // (why would anyone do this is beyond me)

arr.forEach((n,i) => console.log(i,n))
// 0 1
// 1 2
// 2 3
// 10 11

arr.slice().forEach((n,i) => console.log(i,n))
// 0 1
// 1 2
// 2 3
// 10 11

[...arr].forEach((n,i) => console.log(i,n))
// 0 1
// 1 2
// 2 3
// 3 undefined
// 4 undefined
// 5 undefined
// 6 undefined
// 7 undefined
// 8 undefined
// 9 undefined
// 10 11