Is it possible to have a key function as itself when used alone, and as another when used in combination

Question

For example, can I make Space + J act as Ctrl + J, and Space act as Space when pressed on its own?

Answer 1

Yes, you can do this using AutoHotkey (an excellent free keyboard-mapping tool).

Once you download and install AutoHotkey you can create a script file with the following contents:

#NoEnv SendMode Input

~Space & j:: Send ^j

Return

Then just run that script file (right-click, Run Script) and AutoHotkey will send Ctrl+J when you press Space+J, and if you press Space by itself that will pass through just fine.

Answer 2

To add to Nathan's answer, if you don't want to still insert a (space) after using space+J combo, you can use this script:

Space & j:: Send ^j
return
Space:: Send {Space}
return

This will block your space in all combinations, not only the one registered. This will also add a small lag to your space and possibly force you to learn to delay keystrokes after space. Alternatively, you can use Nathan's solution but add a Backspace:

~Space & j:: Send {BS}^j
return

But you must be aware not to use the combinations in cases where space does something more than inserting a space (a space could for example accept autocompletion).