ChakraCore: Functions evaluated in strict mode in console does not prevent implicit variables from being created in Edge

Here we go, this is the specific reason for this behavior:

https://github.com/Microsoft/ChakraCore/blob/master/lib/Runtime/Language/JavascriptOperators.cpp#L3073-L3106

None of this is specced out from what I understand, but at one point a decision was made that when console-eval-ing scripts it shouldn’t “accidentally” pollute the global object, so running x = 1 shouldn’t make global.x == 1. That’s what leaed to this “console scope” being added just above the global, and that’s where these undeclared variables are getting set.

@kfarnung has been looking at undoing some of this since there seems to be a consensus in the browser space that you do in fact pollute the global by assigning to things from inside debuggers, and it looks like the code I highlighted above has been removed in his branch, so with his changes it looks like this behavior will match intuition.

I think I would prefer it to pollute the global scope over the current behavior, myself. Ideally when eval’ing code in the debugger I expect it to work exactly as though the same code were inserted into the source at the point execution is paused—or at least as close to that behavior as possible.

What I don’t understand is that, normally in sloppy mode, any assignment to an undeclared variable automatically becomes global – but in this case it doesn’t. It instead seems to stop at the “near-global” scope you describe, which is bizarre.

Repro in Edge console:

> (function(){"use strict";aa=233})()
< undefined
> aa
< 233
> (Function('return this'))().aa
< undefined

@MSLaguana I can’t reproduce using ch.exe and pure JavaScript eval (not even indirect) which is very frustrating. Best I can tell the issue only manifests when one executes the code in the OP using JsDiagEvaluate.

@infinnie The e command in my SSj debugger uses JsDiagEvaluate and it triggers this bug, too.

I bet the issue is with JsDiagEvaluate, then.

@infinnie We’d like to see a repro scenario in the browser, if possible.

Running the following script in ch.exe:

(function(){'use strict';aa=233;})();
print(aa);

> ch test2.js
ReferenceError: Variable undefined in strict mode
   at Anonymous function (C:\Users\kfarnung\test2.js:1:26)
   at Global code (C:\Users\kfarnung\test2.js:1:2)

Which I believe is the expected behavior.

The plot thickens. It appears this doesn’t actually create a global variable in the usual sense:

@/test.js:1 [anonymous function]
(ssj) e aa
= 233

@/test.js:1 [anonymous function]
(ssj) e global.aa
= "undefined"