Number.isFinite should assert the value is number

[mitchell-merry]

The Number.isFinite() method determines whether the passed value is a finite number — that is, it checks that the type of a given value is Number, and the number is neither positive Infinity, negative Infinity, nor Na

• JSDoc for isFinite

This PR changes isFinite to a type guard for number. Prevents workarounds:

function myFunction(value: unknown) {
  // typeof value === number is redundant here, but required for TS
  if (typeof value === "number" && Number.isFinite(value)) {
    console.log(value); // number
  }
}

Please be nitpicky about the README changes.

Also, the similar functions isInteger, isSafeInteger, and isNan (not sure about the last one) also have the same issue that could be fixed. I'm hesitant to add them all in one go, though.

[mattpocock]

I don't think this is useful, because .isFinite already requires the input to be a number.

[mitchell-merry]

Hi Matt, not too sure what you mean. As far as I can tell, it allows unknown to be passed in:
https://github.com/microsoft/TypeScript/blob/main/src/lib/es2015.core.d.ts#L207

[mitchell-merry]

But, I suppose this would introduce the issue where it would incorrectly narrow in the false case. microsoft/TypeScript#15048

[mattpocock]

@mitchell-merry Aha, you're right! Though yes, I am a bit concerned about introducing too many predicates into ts-reset.