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emscripten-status.rst

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Status of Emscripten compatibility

Hello world test

Quick hello world test:

$ emcc --memory-init-file 0 \
        -s WASM=0 -s POLYFILL_OLD_MATH_FUNCTIONS=1 \
        tests/hello_world.cpp -o /tmp/test.js
$ duk /tmp/test.js

Tweaks needed:

  • --memory-init-file 0: don't use an external memory file.
  • -s WASM=0: disable WebAssembly support, as Duktape doesn't support it.
  • -s POLYFILL_OLD_MATH_FUNCTIONS: don't assume post-ES5.1 Math functions like Math.fround().

Normally this suffices. If you're running Duktape with a small amount of memory (e.g. when running the Duktape command line tool with the -r option) you may need to reduce Emscription "virtual memory" size with the following additional options:

  • -s TOTAL_MEMORY=2097152: reduce total memory size to avoid running out of memory.
  • -s TOTAL_STACK=524288: reduce total stack size to fit it into the reduced memory size.

Changes in Duktape versions:

  • Since Duktape 1.3 there is support for ES2015 TypedArrays which allow Emscripten to run better than with Duktape 1.2, and also allows use of Emscripten fastcomp.

  • Since Duktape 1.5 no fixups are needed to run Emscripten-generated code: Duktape now accepts non-standard unescaped curly braces in regexps, and the Function .toString() output was changed to be acceptable to the Emscripten regexps. Earlier a fixup script was needed:

    $ python $DUKTAPE/util/fix_emscripten.py < /tmp/test.js > /tmp/test-fixed.js
    

Setting up emcc for Duktape

See docker/ for Docker image files which set up a working emcc.

See also