can't narrow from `unknown` to "not a number or bigint" about typescript HOT 7 CLOSED

How difficult it would be to achieve is entirely separate and not something I have knowledge of.

However, I can't conceive of any code where this narrowing would be incorrect, including your example.

from typescript.

I would say this is a design limitation.

unkown is not a union of the types you listed, so the compiler can't narrow the type in the else branch. This would require a type "unknown, except number", which would first require negated types (#4196).

from typescript.

Why isn't unknown a union of all possible types? I would expect it to be a named shorthand for null | undefined | string | boolean | number | bigint | symbol | object since that includes every possible JS value.

from typescript.

See: #39498 (comment)

from typescript.

oof, ok - that issue is actually my precise need for that exact same library. That's very unfortunate.

from typescript.

Consider this working code

function nonNumericTypeof(typeofx: "string" | "boolean" | "symbol" | "undefined" | "object" | "function") {
	return true; 
}

function foo(x: unknown) {
    const t = typeof x;
	if (t === 'number' || t === 'bigint') {
		return false;
	}
    t; // const t: "string" | "boolean" | "symbol" | "undefined" | "object" | "function"
    return nonNumericTypeof(t);
}

Conceivably, type information could embed the results of typeof comparisons (both true and false branches because typeof range is finite) . However, there are reasons why that very hard to integrate into current TypeScript, one of which is that number, string, etc. can be promoted to objects for type comparison.

from typescript.

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

from typescript.