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Class static block does not allow forward reference to static method #45932
Description
Bug Report
🔎 Search Terms
class static blocks, forward reference, incorrect compiler error
🕗 Version & Regression Information
4.4.2 + nightly (4.5.0-dev20210910)
- I was unable to test this on prior versions because the feature is new in 4.4
⏯ Playground Link
Playground link with relevant code
💻 Code
class A {
static {
A.doSomething();
}
static doSomething() {
console.log("gotcha!");
}
}🙁 Actual behavior
Compiler error in line 3: "Property 'doSomething' is used before its initialization.(2729)"
The code works as-is in native JavaScript, tested in Firefox Developer Edition.
The rewrites for class static blocks in Babel as well as in TypeScript itself also work. Both execute the static block's code at a time where static methods of the class are already available.
🙂 Expected behavior
No compiler error, because everything's fine.
A forward reference to a static field, however, should be an error (I guess).
Workaround
Fall back to the way class static blocks could be emulated before they were supported:
Define an unused #-private static constant whose initializer is an immediate-evaluating function.
class A {
static #_ = (() => {
A.doSomething();
})();
static doSomething() {
console.log("gotcha!");
}
}Playground link for workaround
Looks ugly, but works in the desired execution order and produces no compiler error.
Possibly related issues
- Execution order of static field initialization and static initialization blocks is not kept under target: esnext and useDefineForClassFields: false Execution order of static field initialization and static initialization blocks is not kept under target: esnext and useDefineForClassFields: false #45574
- Statements in class static blocks do not narrow types Statements in class static blocks do not narrow types #44949
Activity
fwienber commentedon Sep 20, 2021
Any first evaluation / labels for this one? Maybe Ron Buckton (@rbuckton) or Zzzen (@Zzzen)?
I hope the example code makes the case quite obvious.
fwienber commentedon Nov 10, 2021
Thank you for adding this to 4.6.0 milestone.
I was just wondering why this still has the "needs investigation" label. Do you doubt this is a bug? Do you need further elaboration?
andrewbranch commentedon Nov 10, 2021
Issues are currently coming in faster than I can triage them. It looked like a probable bug to me but I know very little about class static blocks. If I were to take the time to be 100% confident that this is a bug, I would not have time to do the things that need to happen to release TypeScript 4.5. On the other hand, Ron will know if this is a bug within about 30 seconds. “Needs investigation” ~= “Looks suspicious but I defer to the assignee’s judgment, because they have more expertise than me, can devote more time to studying it than me, or both.” Sadly that doesn’t fit in a label.
rbuckton commentedon Nov 10, 2021
Methods should be accessible. Static fields and static blocks are deferred until the end of ClassDefinitionEvaluation after static and prototype methods are defined (including private static elements).
fwienber commentedon Mar 4, 2022
To motivate that this should really be included in the next milestone: It's even worse!
I just found out that from a static code block, you cannot even reference a constant defined before the class:
Run in TypeScript Playground
This results in the unjustified compile error "Variable 'FOO' is used before being assigned.(2454)", but if you still run it, works as it should, logging "FOO".
For this additional case, I can't even think of a work-around, which makes this bug far more serious.
Zzzen commentedon Mar 6, 2022
You are probably the first person in the world who use class static block with TypeScript.
Zzzen commentedon Mar 6, 2022
This is related to #44949. so, you are probably the second one.
fwienber commentedon Mar 30, 2022
This other Playground example is now also fixed when choosing TypeScript "nightly" (4.70-dev...)!
Thanks again for making it work!