Weird Behavior of let: letting a variable to itself while defining the variable renders variable as existed

[Power-tile]

• Version: 12.12.0
• Platform: 10.0.18362 Build 18362 Windows 10, 64 bit
• Subsystem: None, executed in powershell

What steps will reproduce the bug?

$ let a = a; // define a new variable a and assign it with itself, throws ReferenceError
$ a // throws a is not defined
$ let a = 0; // throws Identifier already been declared
$ a // throws a is not defined

Execution process in Powershell:

How often does it reproduce? Is there a required condition?

I tried several times and they all produce the same result.

What is the expected behavior?

I tried running the same code in the browser, and the let a = 0 statement could successfully define the variable a. Screenshot:

What do you see instead?

When executing let a = 0, the environment throws Identifier 'a' already been declared, as shown above.

[devsnek]

Duplicate of #34285

[Power-tile]

#34825 is this issue. Could you clarify which is the original issue that was duplicated?

[devsnek]

oops.

[devsnek]

Duplicate of #8309

[Power-tile]

Thanks for the correction, but after reading #8309 I think these are two different errors. #8309 mentioned that this problem also exists in Chrome console, and I believe the bug was also submitted to Chrome's website. However I tested both on Chrome and Microsoft Edge (which now uses a Chromium core as well), and both of them work as intended:

P.S. This image is from Chrome, and the original image in the description of the issue is from Microsoft Edge.

Interestingly, it worked different in Firefox:

...which did not throw 'a' is undefined when a is queried.

Therefore I believe this is a different bug. Plz look into this, thanks

[bnoordhuis]

@Power-tile It's the same bug but Chromium has since migrated to an alternative REPL mode that doesn't have this issue. Node.js will too (probably), someday, once the quirks have been ironed out.

[Power-tile]

Cool, thanks :D