For...in or For...of

I can never remember which is which when it comes to for...in and for...of.

One iterates over values and one over properties. But which is which? Lucky you, future me, you’ll find out if you keep reading.

The difference

The for…in statement iterates over the enumerable properties of an object, in an arbitrary order.

The for…of statement iterates over values that the iterable object defines to be iterated over.

MDN

Thank you, MDN (always).

In short:

• in for properties
• of for values

Other looping methods

You might want for(), map() or forEach() instead.

See MDN for a few other looping approaches that you might not want.