When using Number.is*, the parameter's type is not inferred as number

[til-schneider]

lib Update Request

Configuration Check

My compilation target is ES2015 and my lib is the default.

Missing / Incorrect Definition

Number.isFinite, Number.isInteger, Number.isNaN and Number.isSafeInteger

Sample Code

function foo(value: number | null | undefined) {
    if (Number.isFinite(value)) {
        bar(value)   // value should be inferred as `number` here
    }
}

function bar (value: number) {
    ...
}

Documentation Link

Number.isFinite

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isFinite

This means only values of the type number and are finite return true.

Number.isInteger

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger

If the target value is an integer, return true, otherwise return false.

Number.isNaN

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN

This also means that only values of the type number, that are also NaN, return true.

Number.isSafeInteger

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger

A Boolean indicating whether or not the given value is a number that is a safe integer.

[til-schneider]

I created a PR that fixes the definition: #44664

[MartinJohns]

This is intentional and there are several existing issues regarding this. Type guards imply that the function matches for all values of the type, but that's not the case for these functions.

[MartinJohns]

See #39090 (comment).

[til-schneider]

Unfortunately it doesn't work, see comments above or #44664.