Repository navigation
let assigment breaks typeof #33462
Description
Activity
Also, you've technically found a bug in firefox. If you feel like it you can report it here: https://bugzilla.mozilla.org/
This is working well for me on Firefox 76.0.1 (64-bit)
Could you share your reproduction steps?
@mariorodriguespt it should be throwing in firefox. This is the same case as
{ typeof x; let x; }It is not throwing on Firefox and it is correct.
It throws an error when you trylet a = a || 2but thetypeofworks as expected.On your example, Firefox does throw an error:
ReferenceError: "can't access lexical declarationx' before initialization"` which is correct due to the order.As far as I can tell, V8 is not handling this correctly: The assignment failed but the
typeofgot broken, this issue is more relevant on a browser environment where you have a second script checking a var usingtypeof.When you do
let x = /* something that throws an error */, the variable is created, but is never initialized. This state is called the "temporal dead zone" (https://snek.dev/blag/2019-07_js_hoisting might help). While a variable is in the temporal dead zone,typeof xwill throw, because the variable exists and is resolvable, but getting its value to try to get the type of it throws a reference error. V8 is behaving correctly here, and firefox has a bug.Just opened a bug on Firefox, I'll leave the link for those interested in the follow up: https://bugzilla.mozilla.org/show_bug.cgi?id=1639078
What steps will reproduce the bug?
How often does it reproduce? Is there a required condition?
Every single time. If you use
letto define a variable and in the assignment part you check if the same variable exists, you won't be able to usetypeofafter.What is the expected behavior?
I would expect
typeofshould always work regardless of the variableaexisting or not.What do you see instead?
Uncaught ReferenceError: a is not defined
Additional information
This appear to be an issue in Chromium since it works as expected in Firefox.