emscripten compiles "regular" C/C++ projects to JavaScript via LLVM. This is how marvels such as PCE.js (A Mac Plus/IBM PC emulator in the browser) can exist. This evening, I've made a few attempts at compiling a number of Tcl versions (from 8.6.1 back to 8.2, didn't get further) using emscripten. The steps for compiling are in theory easy and well-documented . However, emmake make fails every time in the Network code. It fails once when trying to solve "services" to port number (something that can easily be commented away) but also later on in the platform implementation of the socket command. It got too late, so I gave up. Anybody who wants to continue? This should provide an alternative implementation of Tcl in the browser. EF
TP You might want to start smaller. I have compiled and run Picol as an experiment back when emscripten was just getting started. I know of other Tclers who have also compiled Jim. Jim is a good candidate for emscripten, since it is built as a core plus several modules that can be switched on or off with configure directives. To compile Tcl, you will probably have to start with the ./unix/ directory, gut most of the C files in that directory, leaving the internal interfaces but return TCL_ERROR or similar.
EF I am aware of those smaller alternatives. Thing is that I was impressed that the whole "generic" went without any real glitches (or almost). unix didn't seem that bad either... But I'll look into Jim again, as it's much closer to the "real thing" than picol is as far as I can remember.
stevel I've done it to Jim Tcl (see Tcl 2011 paper) but it was slow, although it would be interesting to see how a more recent emscripten would perform. A better approach is Arnulf Wiedemann's APWTCL
TP I was able to compile and run Jim with these steps. You should already have emscripten installed and be able to compile a simple hello world or equivalent, and have the emscripten commands available on your PATH. See Emscripten-SDK . I cloned the jimtcl repository from Github .
cd jimtcl emconfigure ./configure --without-ext="aio load signal" --disable-shared emmake make mv jimsh jimsh.bc emcc jimsh.bc -o jimsh.html
Now load up the jimsh.html page in your browser (e.g., file:///home/user/jimtcl/jimsh.html ). This page has a rudimentary dialog box for standard input, but I found some quirks with it. The first character in the input seems to be discarded, so make sure you preceed input with a space. Type a simple script such as <sp>puts hello Press Ok, then close the dialog box using the window close icon. You will have to close the input dialog box after every line you enter. I'm not sure if this is a bug with the generated stdio interface or perhaps something that emualtes flushing the stdio mechanism in emscripten.