[grumblestumble]

Actually, this is incorrect. You're abusing map here. The purpose of map is to map an existing array onto a new array. You're using map here to mutate properties on nodes in the original array, and creating a new Array, which has the length of the initial array, where each value is the return value of `node.style.background = 'yellow';`

forEach is much more indicative of what you're actually doing here, which is running through an iterable and mutating properties on each node.

Simple rule of thumb: if you're not using the results of `map`, you shouldn't be using it.