add a .then() method to the module-creating function in MODULARIZE

src/postamble.js

@@ -100,6 +100,31 @@ if (memoryInitializer) {
   Module['cyberdwarf'] = _cyberdwarf_Debugger(cyberDWARFFile);
 #endif
 
+#if MODULARIZE
+// Modularize mode returns a function, which can be called to
+// create instances. The instances provide a then() method,
+// must like a Promise, that receives a callback. The callback
+// is called when the module is ready to run, with the module
+// as a parameter. (Like a Promise, it also returns the module
+// so you can use the output of .then(..)).
+Module['then'] = function(func) {
+  // We may already be ready to run code at this time. if
+  // so, just queue a call to the callback.
+  if (Module['calledRun']) {
+    func(Module);
+  } else {
+    // we are not ready to call then() yet. we must call it
+    // at the same time we would call onRuntimeInitialized.
+    var old = Module['onRuntimeInitialized'];
+    Module['onRuntimeInitialized'] = function() {
+      if (old) old();
+      func(Module);
+    };
+  }
+  return Module;
+};
+#endif
+
 function ExitStatus(status) {
   this.name = "ExitStatus";
   this.message = "Program terminated with exit(" + status + ")";

tests/test_browser.py

@@ -2799,20 +2799,38 @@ def test_modularize(self):
     for opts in [[], ['-O1'], ['-O2', '-profiling'], ['-O2'], ['-O2', '--closure', '1']]:
       for args, code in [
         ([], 'Module();'), # defaults
+        # use EXPORT_NAME
         (['-s', 'EXPORT_NAME="HelloWorld"'], '''
           if (typeof Module !== "undefined") throw "what?!"; // do not pollute the global scope, we are modularized!
           HelloWorld.noInitialRun = true; // errorneous module capture will load this and cause timeout
           HelloWorld();
-        '''), # use EXPORT_NAME
+        '''),
+        # pass in a Module option (which prevents main(), which we then invoke ourselves)
         (['-s', 'EXPORT_NAME="HelloWorld"'], '''
           var hello = HelloWorld({ noInitialRun: true, onRuntimeInitialized: function() {
             setTimeout(function() { hello._main(); }); // must be async, because onRuntimeInitialized may be called synchronously, so |hello| is not yet set!
           } });
-        '''), # pass in a Module option (which prevents main(), which we then invoke ourselves)
+        '''),
+        # similar, but without a mem init file, everything is sync and simple
         (['-s', 'EXPORT_NAME="HelloWorld"', '--memory-init-file', '0'], '''
           var hello = HelloWorld({ noInitialRun: true});
           hello._main();
-        '''), # similar, but without a mem init file, everything is sync and simple
+        '''),
+        # use the then() API
+        (['-s', 'EXPORT_NAME="HelloWorld"'], '''
+          HelloWorld({ noInitialRun: true }).then(function(hello) {
+            hello._main();
+          });
+        '''),
+        # then() API, also note the returned value
+        (['-s', 'EXPORT_NAME="HelloWorld"'], '''
+          var helloOutside = HelloWorld({ noInitialRun: true }).then(function(hello) {
+            setTimeout(function() {
+              hello._main();
+              assert(hello === helloOutside); // as we are async, helloOutside must have been set
+            });
+          });
+        '''),
       ]:
         print 'test on', opts, args, code
         src = open(path_from_root('tests', 'browser_test_hello_world.c')).read()