This is a useful trick, but I don't see how it addresses the issue they talked about. As I understand it, they were saying that Firefox and Chrome's Javascript REPL's scroll up through expressions rather than lines. If you say "const f = () => {" and press enter, it doesn't submit it until you close that brace, and when you use the up arrow to scroll back to it later, you get the whole thing (newlines preserved) instead of single lines of it.