Fix emscripten build (#855)

It's not correct to use `--pre-js` and `--post-js` to wrap the module in
a function instance; instead we're supposed to use `-s MODULARIZE=1`.

This still keeps the build as (almost) asm.js, as switching to wasm is a
bit more work (we need to preload the wasm binary module).

This fixes issue #853.

CMakeLists.txt

@@ -397,19 +397,19 @@ else ()
   target_link_libraries(libwabtjs libwabt)
   set_target_properties(libwabtjs PROPERTIES OUTPUT_NAME libwabt)
 
-  set(WABT_PRE_JS ${WABT_SOURCE_DIR}/src/wabt.pre.js)
   set(WABT_POST_JS ${WABT_SOURCE_DIR}/src/wabt.post.js)
   set(EMSCRIPTEN_EXPORTED_JSON ${WABT_SOURCE_DIR}/src/emscripten-exported.json)
 
   set(LIBWABT_LINK_FLAGS
     --memory-init-file 0
-    --pre-js ${WABT_PRE_JS}
     --post-js ${WABT_POST_JS}
     -s EXPORTED_FUNCTIONS=\"@${EMSCRIPTEN_EXPORTED_JSON}\"
     -s RESERVED_FUNCTION_POINTERS=10
     -s NO_EXIT_RUNTIME=1
     -s ALLOW_MEMORY_GROWTH=1
-    -s ELIMINATE_DUPLICATE_FUNCTIONS=1
+    -s MODULARIZE=1
+    -s EXPORT_NAME=\"'WabtModule'\"
+    -s WASM=0
     -Oz
     --llvm-lto 1
   )
@@ -418,6 +418,6 @@ else ()
   set_target_properties(libwabtjs
     PROPERTIES
     LINK_FLAGS "${LIBWABT_LINK_FLAGS_STR}"
-    LINK_DEPENDS "${WABT_PRE_JS};${WABT_POST_JS};${EMSCRIPTEN_EXPORTED_JSON}"
+    LINK_DEPENDS "${WABT_POST_JS};${EMSCRIPTEN_EXPORTED_JSON}"
   )
 endif ()

Makefile

@@ -155,6 +155,10 @@ src/prebuilt/wasm2c.include.c: src/wasm2c.c.tmpl
 src/prebuilt/wasm2c.include.h: src/wasm2c.h.tmpl
 	src/wasm2c_tmpl.py -o $@ $<
 
+.PHONY: demo
+demo: emscripten-release
+	cp out/emscripten/Release/libwabt.js demo
+
 # running CMake
 $(foreach CONFIG,$(CONFIGS), \
 	$(foreach COMPILER,$(COMPILERS), \

demo/wasm2wat/demo.js

@@ -38,7 +38,7 @@ function compile(contents) {
   var foldExprs = foldExprsEl.checked;
   var inlineExport = inlineExportEl.checked;
 
-  wabt.ready.then(function() {
+  WabtModule().then(function(wabt) {
     try {
       var module = wabt.readWasm(contents, {readDebugNames: readDebugNames});
       if (generateNames) {

demo/wat2wasm/demo.js

@@ -20,7 +20,7 @@ Split(["#top-row", "#bottom-row"], {
   direction: 'vertical'
 });
 
-wabt.ready.then(function () {
+WabtModule().then(function(wabt) {
 
 var kCompileMinMS = 100;
 

src/wabt.post.js

@@ -325,17 +325,5 @@ WasmModule.prototype.destroy = function() {
   }
 };
 
-var exports = {
-  ready: Promise.resolve(),
-  parseWat: parseWat,
-  readWasm: readWasm,
-};
-
-if (typeof module !== "undefined" && module && module.exports)
-  module.exports = exports;
-else if (typeof define === "function" && define.amd)
-  define(function() { return exports; });
-else
-  (typeof global !== "undefined" && global || typeof window !== "undefined" && window || this).wabt = exports;
-
-})();  // Call IIFE from wabt.pre.js.
+Module['parseWat'] = parseWat;
+Module['readWasm'] = readWasm;