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Anonymous Function Type Not Constraining Object Return Value #59586
Description
🔎 Search Terms
anonymous function type, return object value
🕗 Version & Regression Information
Same behavior for version 3.9.7, 4.9.5, 5.5.4, 5.6.0-beta and v5.6.0-dev.20240810.
⏯ Playground Link
💻 Code
type ReturnValue = { r: number }
type ParamValue = { p: number }
function f(param: ParamValue): ReturnValue {
return {
r: param.p,
// @ts-expect-error
error: "error",
};
}
f({
p: 0,
// @ts-expect-error
error: "error"
})
type AF = (param: ParamValue) => ReturnValue;
const af: AF = (param:ParamValue) => {
return {
r: param.p,
// @ts-expect-error
error: "error",
};
};
af({
p: 0,
// @ts-expect-error
error: "error"
})🙁 Actual behavior
At third // @ts-expect-error (return object of function af) giving error because it's not used. Since there is no error at that line.
🙂 Expected behavior
Typescript should give error about extraneous error property, since for non-anonymous type function f gave that error. This same error happen for parameter of both af and f function. I assume this should be the case for return value too.
Activity
MartinJohns commentedon Aug 10, 2024
This is working as intended. Your function lacks a return type annotation, so the return type is inferred. The inferred type is then checked for assignability, where excess property checks don't happen anymore.
There are many issues about this.
jcalz commentedon Aug 10, 2024
Duplicate #241 and others
atpur-rafif commentedon Aug 11, 2024
I tried to remove annotation for parameter at anonymous function
af. So, if it's the case (about lack of annotation), then at last// @ts-expect-error(when calling functionaf), it should not throwing any error, because the parameter is inferred. But it still throwing the error.typescript-bot commentedon Aug 15, 2024
This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.