How to replace new line break with '\n'

I'm getting 

Uncaught SyntaxError: Unexpected token ILLEGAL

And I checked that because of this

  currentMd: '<div>#hehe


  </div>'

The two extra new line that is in the currentMd breaking it, so how can I instead replacing that new lines with \n ??

So it will be like this instead

  currentMd: '<div>#hehe\n\n</div>'

In javascript or jQuery would be fine.

It may be not clear that the content is actually just an example here.

The actual content is being retrieved from a database, so in the database there I won't have control and the user will always press enter anyway.

EDIT:

I might have not been very clear on my question here.

The thing is that this content that being assign to contentMd it is being retrieved from nodejs which I have no control on what is going in there.

What about:

var your_content = "<div>#hehe\
    \
    \
    </div>";
var replaced_text = your_content.replace(/\n|\s/g, "");

DEMO: http://jsfiddle.net/A4Hk8/

Go into your text editor and replace the line breaks by hand. Unless this code is computer-generated, or you somehow managed to make this bug in thousands of lines of code before catching it, that should be good enough.

That's exactly how you do it:

> '<div>#hehe\n\n</div>'
"<div>#hehe

</div>"