onRuntimeInitialized is called in Firefox but not in Chrome

[Thomas Grund]

Hello,

(I want to pass large strings (around 100 MB) from JavaScript to C++ in the first place.
This is a really reduced Code to show the problem, even if the code makes no sense anymore.)
The Code IsNotWorking.html is working in Firefox but not in Chrome. Working means, that I can see the two console outputs:

within onRuntimeInitialized
within loadString

The Code IsWorking.html is working in Firefox and in Chrome.
The difference is just two lines which are not needed at all.
Even by just commenting out these two lines, it does not work in Chrome.
I put the code on Github, since there are large strings involved:

https://github.com/ctgrund/Emscripten

Windows 11, emcc 4.0.3, Firefox 139.0.4 64 Bit, Chrome 137.0.7151.104 64 Bit
Can somebody reproduce this?

Thanks for Your help!!

[Sam Clegg]

If you want to be sure that `onRuntimeInitialized` is called you need to set it on the `Module` object before you import the generated code.  Otherwise the runtime could get initialized before you set `Module.onRuntimeInitialized`.

In debug builds you should see a warning when these things happen in the wrong order.  See `consumedModuleProp('onRuntimeInitialized');` for how this is supposed to work.

cheers,

sam

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[Thomas Grund]

Ah ok, it is working now by changing order and putting `var Module={};` in front of `Module.onRuntimeInitialized=function() {...`.

Thanks for explaining!

Thomas

[Sam Clegg]

On Fri, Jun 13, 2025 at 2:05 AM Thomas Grund <thomas.g...@gmail.com> wrote:

Ah ok, it is working now by changing order and putting `var Module={};` in front of `Module.onRuntimeInitialized=function() {...`.

Great!

You could also do `var Module = { onRuntimeInitialized = () => ... }` .

BTW, did you try a debug build?  Can you confirm if you saw the assertion/warning about assigning to onRuntimeInitialized too late?

To view this discussion visit https://groups.google.com/d/msgid/emscripten-discuss/04e61db0-403d-4ab0-a4b3-2b070c2b0eafn%40googlegroups.com.

[Thomas Grund]

I compiled with `emcc -g ...` and did not get any message in the browser console.

[Sam Clegg]

On Sun, Jun 15, 2025 at 12:52 PM Thomas Grund <thomas.g...@gmail.com> wrote:

I compiled with `emcc -g ...` and did not get any message in the browser console.

Did you also compile with `-O0` ?  Or rather, without `-O1` or above? 

To view this discussion visit https://groups.google.com/d/msgid/emscripten-discuss/7b89e309-819b-428f-bc1f-a5a92cf76f8an%40googlegroups.com.

[Thomas Grund]

I checked the `-O0` without getting assertions/warnings.