either

@nick/is/either

isEither

Signature

function isEither<L, R>(
  left: (it: any, ...args: any[]) => it is L,
  right: (it: any, ...args: any[]) => it is R,
): (it: unknown) => it is L | R;

Combine two different predicates into one, such that the resulting function returns true if a given input satisfies either of the two predicates.

This creates a logical OR between the two predicates, narrowing types to a union of the two original predicates' return types. This helps you compose custom reusable type guards with ease, reducing boilerplate and repetition.

Parameters

Name	Info
left	The first predicate to check.
right	The second predicate to check.

Returns

A new predicate that returns true if either left or right are satisfies by a given input.

Category

Composition

Examples

import { isEither, isString, isSymbol } from "@nick/is";

// creating a custom type guard that checks for strings or symbols
const isStringOrSymbol = isEither(isString, isSymbol);
//    ^? const isStringOrSymbol: (it: unknown) => it is string | symbol

// using the custom type guard
isStringOrSymbol("foo"); // true
isStringOrSymbol(Symbol.iterator); // true
isStringOrSymbol(123); // false