Just responding because I found this post via Google and wanted to clarify the solution. I apologize for necro-posting.
The solution specified will add a single space which, depending upon content length and various other things, may or may not create a line break.
The original issue was that the OP was attempting to call the createElement method on the node object, while this method only exists in the document object.
The correct way to do this would be:
var br = document.createElement('br');
obj.appendChild(br);
This code adds a line break at the bottom of the obj object.
Just wanted to clarify that in case someone came across this like I did.