Function optional

The optional schema checks that the type of the value is either the given type, or undefined. It is the equivalent of the TypeScript question mark (?).

Example

import { optional, string } from "typerun/schema";
import { is } from "typerun";

const maybeString = optional(string);
if (is(maybeString)(undefined)) {
  console.log("maybe a string");
}
if (is(maybeString)("hello")) {
  console.log("maybe a string");
}
if (!is(maybeString)(null)) {
  console.log("not maybe a string");
}
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