This is also an issue in vim itself. I think the only way to map just g is to basically map all the other things to <Nop>.

:usage mappings

No cigar:

map g$ <Nop>
map g0 <Nop>
map g<C-g> <Nop>
map g<lt> <Nop>
map g@ <Nop>
map gB <Nop>
map gF <Nop>
map gH <Nop>
map gP <Nop>
map gT <Nop>
map gU <Nop>
map gb <Nop>
map gf <Nop>
map gg <Nop>
map gh <Nop>
map gi <Nop>
map gn <Nop>
map go <Nop>
map gt <Nop>
map gu <Nop>
map zI <Nop>
map zM <Nop>
map zO <Nop>
map zR <Nop>
map zZ <Nop>
map zi <Nop>
map zm <Nop>
map zo <Nop>
map zr <Nop>
map zz <Nop>
noremap z :undo<CR>
noremap g :tn<CR>

still doesn’t work.

Thanks for trying. It's possible that it's mapping specially. In which case a change to the code would be necessary beforehand.

As a reference of sorts:

If a map is not executed, chances are that longer maps starting with the same key sequence still exist.

Take a look at events.js' onKeyPress logic.

Using explicit internal functions:

:js mappings.add([modes.NORMAL], ["g"], "foobar", function() { alert("foobar") });

If a simple g is used, nothing happens, however g<Esc> will execute the function.

Same goes for mappings with keys that are not used anywhere else, such as |:

:js mappings.add([modes.NORMAL], ["|"], "foobar", function() { alert("foobar") });

Now | will execute immediately because there is no other mappings to be resolved.

I don't think adding lots of maps to <Nop> will not help. Nor does unm[ap] seem to do the trick.

If you really want to use g for anything, you may have to remove mappings from the code itself. And there's lots of them, and they come in many shapes.

tl;dr bad idea.

Closing, as this issue doesn't have a "solution" with the current design.

If someone can go through and figure out how to make vimperator actually acknowledge a full set of <Nop> so that the key could be mapped without waiting for the timeout to trigger, we would happily merge such a PR but it is unlikely that any of the "core" developers are going to take any of this on because of our limited constraints on just trying to keep vimperator afloat.