If you are using any of the built-in document query utilities, such as
getElementsByClassName():
> document.getElementsByClassName("some-class")
HTMLCollection(5) [ ... ]Then you are going to get an
HTMLCollection
in response. An instance of this cannot be iterated over, so you cannot call
things like map and filter against it.
To use Array collection methods, you are first going to need to turn the
HTMLCollection into an array. You can do this with
Array.from:
> Array.from(document.getElementsByClassName("some-class"))
[ ... ]