To add the number four to our regular array, we'll type array.push(4), and our console log confirms four is at the end. Let's do "list.push(4)." Notice that our log hasn't changed. Since immutable.js data structures can't be changed in place, we need to reassign the variable to push an item, so we just throw list equals in front.
Methods like concat, that return a new iterable, will behave the same between our standard array and our immutable list. As a side note, in this example, we're using an array which is an iterable object.