Discussion on: 17 Javascript optimization tips to know in 2021 🚀

[Elio Struyf]

Great list, just one thing in tip number 6 foreach Loop Shorthand. A for...in is not the same as a for...of loop!

With the for...in you iterate over the object its properties. For the for...in with an array, you'll get the index value.

With the for...of you iterate over all elements inside the array, so i will be the element and not the index.

[Bruce Axtens]

Thanks for pointing that out, @estruyf . The following deno session demonstrates

> const b = "abcdef".split("")
undefined
> b
[ "a", "b", "c", "d", "e", "f" ]
> for (let x in b) console.log(x)
0
1
2
3
4
5
undefined
> for (let x of b) console.log(x)
a
b
c
d
e
f
undefined