defined.ts

/**
 * Check if the parameter is assigned a value other than undefined or null.
 *
 * Use to improve readability and defend against common mistakes such as `if (!!x)` where it is unclear if the author intended for the check to fail when x is any falsy value such as 0 or -0, or if they intended to check the value is not nullish
 */
export function isDefined<T extends unknown>(x: T | undefined): x is T {
  return x !== undefined && x !== null;
}

/**
 * Check if the parameter is strictly undefined.
 *
 * Use to improve readability and defend against common mistakes such as `if (!x) return;` where it is unclear if the author intended to return early when x is 0 or -0
 */
export function isUndefined<T extends unknown>(
  x: T | undefined,
): x is undefined {
  return x === undefined;
}

type Nullish = null | undefined;
/**
 * Check if the parameter is nullish
 */
export function isNullish<T>(x: T | Nullish): x is Nullish {
  return x == null;
}