Yes, sure. Many languages have them now. (I'm not sure what TCL looked like in 1995. SUN actually had an idea to promote TCL for both frontend and backend work, but then Java happened.)
Tk debuted in 1993, so I presume Tcl's event loop features were in place by then.
IMO Tcl would have been a vastly preferable choice for a browser scripting language. Text is its native data type, and would have minimized impedance mismatches with other functional areas of the text-based HTML/HTTP environment. Also it would have been far easier for newbies to get started with web script hacking. At the time JavaScript seemed like alien algebra to a lot of non-computer science majors.
IMO Tcl would have been a vastly preferable choice for a browser scripting language. Text is its native data type, and would have minimized impedance mismatches with other functional areas of the text-based HTML/HTTP environment. Also it would have been far easier for newbies to get started with web script hacking. At the time JavaScript seemed like alien algebra to a lot of non-computer science majors.