Crash when a class closes over lexically-bound variables inside an eval

[shicks]

Steps to reproduce in Edge 13:

Point browser to a page serving the following JS file:

eval('(function(){let a; class A { x() { return a; } } })()');

This will cause the page to fail to load, immediately reloading the HTML and JS from the server a second time, and then giving up with a message of "This page is having a problem loading. We tried to load this page for you a few times ...".

The crash can be averted in any of several different ways:

1. Remove the eval - the code itself works fine outside an eval
2. Change let to var - no problems there [note that changing to const (and assigning something, as required) does not prevent the crash]
3. Change the method to a function (i.e. remove the class) - ordinary functions have no problems
4. Remove the IIFE - top-level lets seem to be fine, too
5. After a crash, open devtools (F12), highlight the URL, and hit enter - may take a few tries before it finally succeeds, but once it does, it continues to succeed

The crash appears to be independent of strict mode - adding "use strict"; either at the beginning of the eval, or immediately inside the function - neither makes a difference.

[ianwjhalliday]

Thanks for reporting this bug @shicks

It has already been fixed in ChakraCore and will be included in the next release of Edge. If I am not mistaken it should also be fixed in the latest preview builds of Windows too.