Suggestion: narrower parameters for NumberConstructor

[danvk]

TypeScript Version: 2.6.2

Code

function foo() {
    return 1234;
}

const num = Number(foo);
// intent was probably:
// const num = foo();

Expected behavior: Number(foo) should be an error.

Actual behavior: Type checks. num is NaN at runtime.

I assume this is WAI, but figured I'd ask. This came up when I got a type error in a math expression, something like 2 * box.width. I didn't read the error closely and assumed the issue was that box.width was a string. So I made it 2 * Number(box.width). This made the error go away, but introduced NaNs at runtime.

Number is declared as:

const Number: NumberConstructor(value?: any) => number

could we make this narrower? maybe

const Number: NumberConstructor(value?: string|number|Date|boolean) => number

[RyanCavanaugh]

The "uncalled function" problem is more broad than Number(x); we speculate about a type that means "anything except a callable function" that would be the input type to a lot of coercion operators, though the existence of classes with static properties really muddies the waters. It's arguable that the object type should have excluded function types, even though (function() { }) instanceof Object is true.

Anyway "pass it to Number" is sort of the "big hammer" to coerce anything to a number and we'd rather not break legit (if odd) uses of that function.

In conclusion, JavaScript is a land of contrasts.