Can you explain the difference between Function and (...args: any[]) => any?
I recently discovered that Function cannot be assigned to (...args: any[]) => any. Why is that so puzzling?
declare let foo: Function;
declare let bar: (...args: any[]) => any;
bar = foo;
// ~~~
// ^^^
// Type 'Function' is not assignable to type '(...args: any[]) => any'.
// Type 'Function' provides no match for the signature '(...args: any[]): any'. (2322)
It seems that the Function interface does not include a callable signature in its declaration. However, if you have an object of type Function, you can call it as long as it is treated as (...args: any) => any. There is an open issue, which may be a bit outdated, at microsoft/TypeScript#20007, requesting a change to this behavior. A comment on the issue states:
The original purpose of the
Functioninterface was for it not to be callable. In other words,Functionin relation to function types should be similar tounknownin relation to other types, not callable. We have relaxed this restriction by allowingFunctionto behave as callable in the compiler through special handling. It has been suggested to make this a--noImplicitAnyerror because callingFunctions can be unsafe.
If you are passionate about this issue, consider visiting the linked issue and expressing your support 👍 while explaining your use case. Realistically, however, the chances of it being changed are slim, so it might be best to acknowledge the discrepancy and move forward.
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