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Lack of type checking for callback parameters #15579
Description
TypeScript Version: master
Code
function f(g: (ev: Event) => any) { }
function g(ev: MouseEvent) { }
f(g);
f(ev => g(ev));Expected behavior:
$ node built/local/tsc.js index.ts --noEmit --strict
index.ts(3,3): error ...
index.ts(4,11): error TS2345: Argument of type 'Event' is not assignable to parameter of type 'MouseEvent'.
Property 'altKey' is missing in type 'Event'.
Actual behavior:
$ node built/local/tsc.js index.ts --noEmit --strict
index.ts(4,11): error TS2345: Argument of type 'Event' is not assignable to parameter of type 'MouseEvent'.
Property 'altKey' is missing in type 'Event'.
Activity
mhegazy commentedon May 5, 2017
https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-function-parameters-bivariant
falsandtru commentedon May 6, 2017
I didn't know that well because the FAQ doesn't say specific definitions of types of Animal and Dog. But it seems like you can keep the consistency of
f(g)andf(ev => g(ev)). Are you really choosing the current inconsistency?RyanCavanaugh commentedon May 8, 2017
Suffice to say we've thought about this problem a lot and are sticking with the current situation.