bar is expected to be a function with no return value:
let foo = () => 'foo';
let bar: () => void = foo; // produces no error
Can bar be prevented from being assigned with a function that doesn't match expected () => void signature?
For example, in this case:
declare let jsApiThatShouldNeverAcceptTypeofFoo = (bar: () => void) => void;
jsApiThatShouldNeverAcceptTypeofFoo(bar);
A partial workaround is to ensure that the return type of the function has no keys. This is satisfied by void, but also by {} and never. This might be close enough, as functions retuning never should throw an error and functions returning {} happen infrequently enough:
type EnsureVoid<T> = keyof T extends never ?
void
: "Should not have a return type, only ()=> void is allowed";
declare let jsApiThatShouldNeverAcceptTypeofFoo: <T extends EnsureVoid<T>>(bar: ()=> T) => void;
let foo = () => 'foo';
jsApiThatShouldNeverAcceptTypeofFoo(foo) // Error
let bar = () => { };
jsApiThatShouldNeverAcceptTypeofFoo(bar)
let baz = () => ({ });
jsApiThatShouldNeverAcceptTypeofFoo(baz)
let boo = () => { throw "Error" };
jsApiThatShouldNeverAcceptTypeofFoo(boo)
Collected from the Internet
Please contact [email protected] to delete if infringement.
Comments