Error Functions

An error function is a function that is created to do something with errors. They allow the user to do something about errors.

Throw If

A function that will throw an error when something is true.

function throwIf(
  condition: boolean,
  message = 'Something went wrong',
): asserts condition is false;

Usage

const user = fetch('https://jsonplaceholder.typicode.com/users/1')
  .then((response) => response.json())
  .then((json) => json);

throwIf(!user, 'There is not user here');

Throw Unless

function throwUnless(
  condition: boolean,
  message = 'Something went wrong',
): asserts condition;

Usage

const user = fetch('https://jsonplaceholder.typicode.com/users/10')
  .then((response) => response.json())
  .then((json) => json);

throwUnless(user, 'There is not user here');

Return Error and Result From Promise

A function that returns a potential result and a potential error. This is useful for checking if a result is returned or it's an error.

function returnErrorAndResultFromPromise<T extends Promise<any>>(
  cb: T,
): Promise<readonly [Awaited<T>, null] | readonly [null, Error]>;

Usage

const [result, error] = returnErrorAndResultFromPromise(
  fetch('https://jsonplaceholder.typicode.com/users/10').then((response) =>
    response.json(),
  ),
);

if (error) {
  throw error;
}

console.log(result);