Nullish

Overview

The Nullish type indicates the absence of a value or signifies that a variable has not been initialized.

It's purpose is to handle optional properties, variables or function parameters that may no always have a value. It helps enhance the reliability of the code by explicitly handling there null or undefined cases.

Syntax

type Nullish = null | undefined;

Examples

Example #1

type Form = {
  email: string | Nullish;
  password: string | Nullish;
};

Example #2

function isNullish(value: unknown): value is Nullish {
  return value === null || value === undefined;
}

const value = [1, 2, 3, null, 5, 6, undefined];

if (value.some(isNullish)) {
  throw new TypeError('there is a null or undefined type.');
}