🚨 Error: Uncaught ReferenceError: prompt is not defined

[ampprojectbot]

Details

Error report: link
First seen: Apr 15, 2020
Frequency: ~ 48689/day

Stacktrace

Error: Uncaught ReferenceError: prompt is not defined
    at (uncaught-referenceerror-prompt-is-not-defined.js:1)

[rcebulko]

This appears to only be occurring on the domain https://hindi-news18-com.cdn.ampproject.org, (example page) so far, or at least that's the bulk of the reports. The publisher has code like the following:

function checkCookie()
        {
          var user = accessCookie("testCookie");
          if (user!="")
        	alert("Welcome Back " + user + "!!!");
          else
          {
            user = prompt("Please enter your name");
            num = prompt("How many days you want to store your name on your computer?");
            if (user!="" && user!=null)
            {
            createCookie("testCookie", user, num);
            }
          }
        }
		createCookie("JioPlayer","1",1);
		checkCookie();//# sourceURL=amp-script%5Bsrc=%22https://hindi.news18.com/amp-customjs.js?v=1%22%5D.js

This is within an amp-script[src=...] script. A few takeaways:

1. According to the compatibility table, the Window.prompt API is not enabled in the worker DOM. Would it be feasible to stub blocked APIs in some way to alert publishers that they will fail?
2. Errors occurring in an amp-script throw stacktraces outside of our code. Example:

Uncaught ReferenceError: prompt is not defined
    at checkCookie (amp-script[src="http…omjs.js?v=1"].js:28)
    at amp-script[src="http…omjs.js?v=1"].js:37

The amp-script stacktrace bit could be ignored on the error-reporting backend, but the runtime error handling should be able to handle these errors separately and report them as user errors.

/cc @ampproject/wg-runtime

[stale]

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