Show warnings when switch from VB to SaaS page

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Hi,

We implemented the auto save on extension built using VB and extension is integrated on SaaS. Have a requirement on one of the forms to check all the mandatory fields are filled before switching on SaaS (HR help desk) page. As we know before Exit won't be fired if we navigate to another page outside of a VB app.
It works only if users are on VB app.

So just thinking do we need to use JS to identify the mouse pointer is outside of the VBCS page and show the warning if value not entered for all the mandatory fields or is there any better ways to achieve this?