It’s Markdown syntax. You can actually format it nicely in a code block:

bool isEven( long long x ) {
  if ( x < 0 ) x = -x;
  if ( x == 1 )
    return false;
  if ( x == 2 )
    return true;
  return isEven( x - 2 );
}

You do that by adding ``` above and below it. To force single line breaks, you can terminate your sentences with two spaces, or a backslash.

Can you put this in a npm package so I can use it in my project, please?

Is this meant to be a joke or is it intended to be a serious solution?

Asking for someone who lacks a sense of humor.

Ok, fine, I'm asking for me. That person is me.

I love the use of recursion. Slick.

For large numbers, you might get a stack overflow. Depends on whether the compiler recognizes that it's a tail recursion and then handles it appropriately.

As for why Lemmy ignores single newlines, that's because it uses Markdown for its comment syntax, which happens to handle newlines that way. If you want a single newline to display, you have to add two spaces at the end of the line.

Here, you really would have wanted to use a code block, though, which you can create with backticks

```
like
so.
```

Normally, this would display "like so." in a monospace font and handle newlines as you expected:

like
so.

Some quirk of this version of Markdown I think.
Try putting two spaces at the end of a line before your single newline.