Why did confirm and alert and ie11 stop working?

Question

JavaScript

Please, prompt
There is a web application in a local area network, 2 years worked normally. Yesterday there were complaints from users that it does not work. I began to understand, it turned out that in IE11 the Javascript confirm and alert stopped working. And IE is the main browser in the company.
There are no problems in Chrome and Mozilla.
Began to test on the localhost, it works out very strangely. The same page in one tab alert does not show, copied the address, opened it in another tab - it gives out normally.
I began to look at the security settings in IE, allowed all scripts to the maximum. Does not help.
Either the admin messed up with group policy, or a crooked update arrived in IE.
Where to dig and what can be done?

Answer 1

Check the console for any errors. Most likely, the execution does not reach the code with alert, due to another error. If the alert is shown on other pages, then that's the point. Also, on the page where the alert does not work, you can try to display it manually by simply typing alert("Hello world!") into the console.