Thanks for clarifying this and it is working now with encoding set to UTF-8. One advantage is the smaller file size. Another small point that comes up: The output file (here Sum.js) is not a text file anymore in the sense that the file contains zero bytes \x00 now. So for handling this (load Sum.js and copy it to another html file) we have to switch to binary file handling which is not a problem at all.
Thanks again Thomas jj schrieb am Montag, 3. November 2025 um 15:05:46 UTC+1: > Thanks for reporting this. > > This was due to a planned change, although we did not sufficiently > highlight what is going on in this case. > > Recently we migrated the SINGLE_FILE mode to no longer use base64, but > directly embed the binary content in a UTF-8 encoded string. However, this > change requires that the served files are explicitly annotated to be > encoded as UTF-8, or otherwise browsers default to legacy behavior, and > assume Windows CP1252 encoding. (maybe on Windows only, not completely sure) > > A quick fix is to add <meta charset='utf-8'> in the <head> section of the > above index.html. That will cause the browser to change the defaults also > for all downloaded .js files to UTF-8. > > The PR https://github.com/emscripten-core/emscripten/pull/25134 > internally addressed the change in encoding, and I was thinking that would > transparently cover every use case. I.e. originally I had a mindset that > users of SINGLE_FILE would all be doing "-sSINGLE_FILE -o foo.html", i.e. > they'd be generating a single .html file as output. > > Though in your above example, you are doing "-sSINGLE_FILE -o foo.js", to > use the single file mode in a "two file" mode, by then manually providing a > index.html file. That use then would not automatically get the UTF-8 > encoding declaration. > > Testing locally, I see that adding <meta charset='utf-8'> in the <head> > section fixes up the test case. > > Authored a PR https://github.com/emscripten-core/emscripten/pull/25704 to > help users be aware that declaring the UTF-8 encoding is now explicitly > necessary for SINGLE_FILE mode - the legacy Windows CP1252 will > unfortunately no longer work with SINGLE_FILE in binary encoding mode. If > Windows CP1252 is needed for some reason, one can still fall back with > -sSINGLE_FILE_BINARY_ENCODE=0 like Sam mentioned. > > On Friday, October 31, 2025 at 11:37:32 PM UTC+2 [email protected] wrote: > >> BTW, if you want to get things working quickly you should be able use >> `-sSINGLE_FILE_BINARY_ENCODE=0`. This setting was added specifically in >> case a bug this showed up/ >> >> cheers, >> sam >> >> On Fri, Oct 31, 2025 at 8:54 AM Thomas Grund <[email protected]> >> wrote: >> >>> Thanks for analyzing! >>> >>> Thomas >>> >>> [email protected] schrieb am Donnerstag, 30. Oktober 2025 um 18:32:45 >>> UTC+1: >>> >>>> Thanks for reporting, this turns out ot be a recent regression in >>>> SINGLE_FILE. I bisected to >>>> >>>> https://github.com/emscripten-core/emscripten/pull/25599 >>>> >>>> and posted there. >>>> >>>> - Alon >>>> >>>> >>>> On Thu, Oct 30, 2025 at 6:02 AM Thomas Grund <[email protected]> >>>> wrote: >>>> >>>>> Hello, >>>>> >>>>> The following example does >>>>> >>>>> - not work with current emcc 4.0.18 in Chrome. >>>>> >>>>> It >>>>> >>>>> - works with current emcc 4.0.18 in Firefox and it >>>>> - works with emcc 4.0.16 in Chrome. >>>>> >>>>> I use local files on Windows 11. >>>>> >>>>> Example index.html: >>>>> <!DOCTYPE html> >>>>> <html> >>>>> <head> >>>>> <script> >>>>> function compute() { >>>>> a=parseFloat(document.getElementById('a').value); >>>>> b=parseFloat(document.getElementById('b').value); >>>>> document.getElementById('c').innerText = Module.Sum(a, b); >>>>> } >>>>> </script> >>>>> <script src="Sum.js"></script> >>>>> </head> >>>>> <body> >>>>> <input id="a" type="number" onchange="compute()"> >>>>> <input id="b" type="number" onchange="compute()"> >>>>> <div id="c">Result</div> >>>>> </body> >>>>> </html> >>>>> >>>>> Example Sum.cpp: >>>>> #include <emscripten/bind.h> >>>>> >>>>> double Sum(double a, double b) { >>>>> return a+b; >>>>> } >>>>> >>>>> EMSCRIPTEN_BINDINGS(Module) { >>>>> emscripten::function("Sum", &Sum); >>>>> } >>>>> >>>>> Compile with: >>>>> emcc -o Sum.js Sum.cpp -sSINGLE_FILE --bind -sASSERTIONS >>>>> >>>>> Error in Chrome Console: >>>>> failed to asynchronously prepare wasm: CompileError: >>>>> WebAssembly.instantiate(): section was shorter than expected size (18371 >>>>> bytes expected, 207 decoded) @+219 >>>>> instantiateArrayBuffer @ Sum.js:634 >>>>> await in instantiateArrayBuffer >>>>> instantiateAsync @ Sum.js:645 >>>>> createWasm @ Sum.js:713 >>>>> (anonymous) @ Sum.js:2761Understand this error >>>>> Sum.js:275 Uncaught (in promise) TypeError: filename.startsWith is not >>>>> a function >>>>> isFileURI @ Sum.js:275 >>>>> instantiateArrayBuffer @ Sum.js:637 >>>>> await in instantiateArrayBuffer >>>>> instantiateAsync @ Sum.js:645 >>>>> createWasm @ Sum.js:713 >>>>> (anonymous) @ Sum.js:2761Understand this error >>>>> Sum.js:794 still waiting on run dependencies: >>>>> (anonymous) @ Sum.js:794 >>>>> setInterval >>>>> addRunDependency @ Sum.js:784 >>>>> createWasm @ Sum.js:674 >>>>> (anonymous) @ Sum.js:2761Understand this error >>>>> Sum.js:796 dependency: wasm-instantiate >>>>> (anonymous) @ Sum.js:796 >>>>> setInterval >>>>> addRunDependency @ Sum.js:784 >>>>> createWasm @ Sum.js:674 >>>>> (anonymous) @ Sum.js:2761Understand this error >>>>> Sum.js:799 (end of list) >>>>> (anonymous) @ Sum.js:799 >>>>> setInterval >>>>> addRunDependency @ Sum.js:784 >>>>> createWasm @ Sum.js:674 >>>>> (anonymous) @ Sum.js:2761Understand this error >>>>> >>>>> What am I doing wrong? >>>>> >>>>> Thanks for your help! >>>>> Thomas >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "emscripten-discuss" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To view this discussion visit >>>>> https://groups.google.com/d/msgid/emscripten-discuss/504419d6-cdcf-4eec-9a1e-e7f69f87a129n%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/emscripten-discuss/504419d6-cdcf-4eec-9a1e-e7f69f87a129n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "emscripten-discuss" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> >> To view this discussion visit >>> https://groups.google.com/d/msgid/emscripten-discuss/5b591cef-ad8e-467f-95dc-b43719e21086n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/emscripten-discuss/5b591cef-ad8e-467f-95dc-b43719e21086n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. 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