remove the unnecessary legacy Module parameter to integrateWasmJS. this made debugging some startup issues harder (as the outside Module could be erroneously replaced, but not the one captured as the parameter. also add a specific check in ASSERTIONS mode for such erroneous replacing of Module (#5595)

Author: kripken

src/preamble.js

@@ -2088,7 +2088,7 @@ var cyberDWARFFile = '{{{ BUNDLED_CD_DEBUG_FILE }}}';
 #endif
 
 #if BINARYEN
-function integrateWasmJS(Module) {
+function integrateWasmJS() {
   // wasm.js has several methods for creating the compiled code module here:
   //  * 'native-wasm' : use native WebAssembly support in the browser
   //  * 'interpret-s-expr': load s-expression code from a .wast and interpret
@@ -2310,11 +2310,21 @@ function integrateWasmJS(Module) {
 #if BINARYEN_ASYNC_COMPILATION
 #if RUNTIME_LOGGING
     Module['printErr']('asynchronously preparing wasm');
+#endif
+#if ASSERTIONS
+    // Async compilation can be confusing when an error on the page overwrites Module
+    // (for example, if the order of elements is wrong, and the one defining Module is
+    // later), so we save Module and check it later.
+    var trueModule = Module;
 #endif
     getBinaryPromise().then(function(binary) {
       return WebAssembly.instantiate(binary, info)
     }).then(function(output) {
       // receiveInstance() will swap in the exports (to Module.asm) so they can be called
+#if ASSERTIONS
+      assert(Module === trueModule, 'the Module object should not be replaced during async compilation - perhaps the order of HTML elements is wrong?');
+      trueModule = null;
+#endif
       receiveInstance(output['instance']);
     }).catch(function(reason) {
       Module['printErr']('failed to asynchronously prepare wasm: ' + reason);
@@ -2527,7 +2537,7 @@ function integrateWasmJS(Module) {
   var methodHandler = Module['asm']; // note our method handler, as we may modify Module['asm'] later
 }
 
-integrateWasmJS(Module);
+integrateWasmJS();
 #endif
 
 // === Body ===