Webviewer freezes with warning: Blocking on main thread is dangerous

WebViewer Version: 7.3.0

I am experiencing an issue with regards to webviewer, It seems that when the viewer is incrementally downloading a pdf file, and then the user attempts to do another action on the page (in app’s our case it is to select another pdf file to view) the browser freezes abruptly.

I checked the console log and I saw this particular warning is coming from CoreControls.js

I would appreciate it if anyone can point me in the right direction on how to prevent and/or handle this kind of warning

Hello, I’m Ron, an automated tech support bot :robot:

While you wait for one of our customer support representatives to get back to you, please check out some of these documentation pages:



We’re looking into this, thanks for your patience.



Our Core team is working on this, and the workaround now is to switch the backendType. There’re are two types of backendType - ems and wasm-threads you can choose from.



Do you see 404 error in the network tab when this happens? Thanks.


Hi there, thanks for reaching out!

No There isn’t any 404 message that is appearing in the network tab in that particular session.

It seems changing the backendType to ems works. I haven’t seen the warning once in latest test session. I will test further and get back to you. Thanks!