Microsoft/TypeScript
Voir sur GitHub"Used before initialization" error false positives and negatives with optional properties
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#61 785 ouverte le 30 mai 2025
BugDomain: check: Control FlowHelp Wanted
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Description
🔎 Search Terms
used before its initialization
🕗 Version & Regression Information
- This changed between versions 4.2.3 and 4.3.5
- This changed in commit or PR #43100 (
0967f3b)
⏯ Playground Link
💻 Code
class C {
a = this.b;
b?: number = 123;
}
class D {
a: number | undefined;
b = this.a = 123;
}
🙁 Actual behavior
When initializing C.a: no error.
When initializing D.b:
Property 'a' is used before its initialization. (2729)
🙂 Expected behavior
When initializing C.a:
Property 'b' is used before its initialization. (2729)
When initializing D.b: no error.
Additional information about the issue
Tried with both useDefineForClassFields set to true and false.
The behavior is as expected when switching the use of undefined and the "optional" ? modifier like this:
class C {
a = this.b;
b: number | undefined = 123;
}
class D {
a?: number;
b = this.a = 123;
}
#43100 seems to have taken a wrong approach. Instead of basing the decision to report an error on whether the ? modifier is present, it should be based on whether the property access is on the left-hand side of an assignment expression.