MODULARIZE & EXPORT_NAME build options oddities

Consider

$ emcc tests\hello_world.c -s MODULARIZE=1 -o a.html

This produces a web page that does not run, but gives no build errors either.

There are two things that are odd about the generated build.

First, I think the history of -s MODULARIZE=1 was intended to be primarily used when building to JavaScript with -o a.js, so the intent is that one would manually invoke the generate Module() function (defined with -s EXPORT_NAME= option) to start the app. But when one is targeting HTML with any of the default html shell files that Emscripten provides (no --shell-file directive passed, or --shell-file src/shell_minimal.html) it seems that we should be automatically be generating a Module(); invocation there to start the page.

Second, why is the default value of the -s EXPORT_NAME= option called Module? That seems wrong. Module is supposed to be an object that contains import/export interactions with the generated page. In MODULARIZE mode EXPORT_NAME specifies the name of the function that one should call to launch the page. Calling this function also Module seems like we are calling two different things by the same name, and by default, one would need to call Module(Module); to run the page. Hence when building

$ emcc tests\hello_world.c -s MODULARIZE=1 -o a.html

it is not possible to launch the generated build even from web console.

Perhaps default value of EXPORT_NAME should be changed to something like 'EmscriptenCode', so that the default launch sequence would look like EmscriptenCode(Module);, and our default shells would add a {{{ EXPORT_NAME }}}(Module); directive to them?

Hmm, further, docs in settings.js say

// page, it will use the global scope. With MODULARIZE set, we will instead emit
//
//   var EXPORT_NAME = function(Module) {
//     Module = Module || {};
//     // .. all the emitted code from emscripten ..
//     return Module;
//   };
//
// where EXPORT_NAME is from the option of the same name

However if I do a -s MODULARIZE=1 -s EXPORT_NAME='EmscriptenCode' build, then I don't get

var EmscriptenCode = function(Module) {
  Module = Module || {};
  // .. all the emitted code from emscripten ..
  return Module;
};

in my build. But instead I get

var EmscriptenCode = (function() {
  return (function(EmscriptenCode) {
    EmscriptenCode = EmscriptenCode || {};
    ...
    return EmscriptenCode;
  });
})();

which seems unnecessary - the inner Module should not need to change to EmscriptenCode?

MODULARIZE by itself does not run the code, yes - intentionally, so you can instantiate it multiple times later as needed.

MODULARIZE_INSTANCE will create an instance for you, and call it (so you can't create more than one).

About the name being replaced in more places - yeah, that might be redundant, maybe we did it for aesthetic purposes. I'm not sure - may need to look through the PRs.

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 7 days. Feel free to re-open at any time if this issue is still relevant.

See this is closed, but still a little confused, not being a JS expert. If I build with -s MODULARIZE=1 -s EXPORT_NAME='"createModule"' -s MODULARIZE_INSTANCE=1 --shell-file "shell_minimal.html" in the HTML there is an object created called Module :

      var Module = {
        preRun: [],
        postRun: [],
...

but I dont think it gets used at

...
  return createModule
}
)(typeof createModule === 'object' ? createModule : {});
if (typeof exports === 'object' && typeof module === 'object')
      module.exports = createModule;
    else if (typeof define === 'function' && define['amd'])
...

Would I be right in saying that

the Module created in shell_minimal.html is not used
To use Module created in shell_minimal.html I should drop -s MODULARIZE_INSTANCE=1 and pass it in to createModule e.g.

createModule(Module);

Which I could put in shell_minimal.html ?

@yowl

@yowl note that MODULARIZE_INSTANCE was recently removed. it did lead to complicated situations like this one. You can do similar things by manually creating an instance, which avoids the possible confusion between the generator function (createModule in your example) and the parameters to that function, which are Module in that shell file.

In general I think the default html shell files just set values to Module, so they are not aware of MODULARIZE or EXPORT_NAME - you may need a custom html in some cases.

Fix -sMODULARIZE + html output. NFC

Fix -sMODULARIZE + html output. NFC (#26173)

Fix -sMODULARIZE + html output. NFC (emscripten-core#26173)

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MODULARIZE & EXPORT_NAME build options oddities #7950

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MODULARIZE & EXPORT_NAME build options oddities #7950

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juj commented on Jan 29, 2019

kripken commented on Jan 29, 2019

stale commented on Jan 29, 2020

yowl commented on May 17, 2020

kripken commented on May 18, 2020

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