Double WASM file download - any reason?

By monitoring our user’s activity, sometime we can see that the WASM files are downloaded twice when connecting to Zoom.
But sometime it’s not happening.

Through the monitoring i noticed that when it happens,

  • the first download is the one triggered by the code itself (loading the WASM libraries before initializing zoom connection & joining a meeting)
  • the second one happens during the join operation

So, would you mind to explain us why this happen / not happen in order to understand better how the web SDK deals with WASM file ? Is this due to WASM check / ensure download system introduced in 1.7.10 (if i remember well), or that’s not related at all ?

Not really an error, just wonder why sometime it double download these specific resources.

Which version?

To Reproduce(If applicable)
Just run any zoom application i guess, your demo application should reproduce it as well.

Double download case (i had to hide the path sorry, just trust me these are the WASM resources).

Device (please complete the following information):

  • Browser: Latest chrome version - but not related.

After discussing about this with a colleague, we wonder if this could be a bug on the monitoring tool.

The downloaded size versus speed on the second calls seems too fast compared to first one. It might be a browser cache hit reported as a real call instead.

Can you please tell us whether you have such twice call in the web SDK code or not to clarify this ?

Hey @nvivot,

Thank you for reaching out to the Zoom Developer Forum. I attempted to reproduce this behavior with our Sample App on Chrome Version 87.0.4280.88 but saw that the WASM files were only requested on the initialization of the ZoomMtg object.

The downloaded size versus speed on the second calls seems too fast compared to first one. It might be a browser cache hit reported as a real call instead.

I think you’re on the right track in terms of investigating this as a Cache Hit being misinterpreted by the monitoring tool you’re using. If you find any details that indicate otherwise, please update me here and I’ll look into this further.


Hi @MaxM,

For the cache hit misinterpretation we are pretty sure it is an issue with the monitoring tool yes.

But what we don’t understand is why sometime Zoom initialization is triggering a second time the download of the WASM files (this happen right after the ping requests on the gateways)

Hey @nvivot,

Thank you for your question. I think there might have been a misunderstanding. I was mentioning that since I don’t see the same behavior on my end, it looks like the files are requested twice because of an issue with the monitoring tool.

If this isn’t the case, and you’re seeing those files requested even in the browser console, would you be able to share a Git repo that has code that exhibits the issue?


Hey @nvivot,

I reached out to a senior colleague on my team and he was able to point me in the right direction for this issue. I’ve since submitted this for review to our engineering team. As soon as I hear back from them I’ll be sure to update you. (CS-2668)


So far i cannot reproduce it but it still see this happening on our user’s monitoring (very rare but still)

I’ll contact the monitoring tool support and ask them to also investigate on their side.


Thanks @nvivot. We will let you know what we find on our end.


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