OK, so I use the emdash as follows: someword---anotherword, but the problem is this prevents hyphenation of both words around the dash. I can fix this by replacing --- with \textemdash, but I was wondering, is there any way to redefine the --- "command" with \textemdash?
I use LuaTeX. Related to this issue issue I've found this and this, but neither provides an acceptable solution...
Thanks in advance!

some\-word---another\-word. But clearly that's not the general solution you seek. – Thruston Aug 29 '13 at 21:19someword{}---{}anotherword, but again not general... – Thruston Aug 29 '13 at 21:31extdashpackage. The reason this is hard is that the --- is defined as a ligature deep down in the TeX fonts rather than as a macro. – Thruston Aug 29 '13 at 21:47