karol-majewski

import { mapValues } from 'lodash';

declare module 'lodash' {
  interface LoDashStatic {
    mapValues<T extends object, TResult>(object: T, callback: (value: T[keyof T], key: keyof T, collection: T) => TResult): { [K in keyof T]: TResult };
  }
}

interface FatalErrors {
  500: boolean;

karol-majewski

/**
 * These are necessary to construct `enumerate`
 */
type ValueOf<T> = T[keyof T];

type NonEmptyArray<T> = [T, ...T[]]

type MustInclude<T, U extends T[]> =
  [T] extends [ValueOf<U>]
    ? U

karol-majewski

published: true

karol-majewski

A short tale about API design

When I was using why-did-you-render, I noticed something strange. There were hundreds of wasted renders happening on the Collections page of Unsplash. One of the components, called SmallTag, was particularily active.

I used React DevTools to find out which DOM nodes it was rendering.

karol-majewski

import * as React from 'react';

type Primitive =
  | boolean
  | number
  | bigint
  | string
  | symbol
  | null
  | undefined;

karol-majewski

function assertServiceWorkerGlobalScope(
  self: typeof globalThis,
): asserts self is typeof globalThis & ServiceWorkerGlobalScope {
  if (self.navigator.serviceWorker.controller === null) {
    throw new Error('Service worker code can be executed only in a service worker context.');
  }
}

assertServiceWorkerGlobalScope(self);

karol-majewski

/**
 * @author https://stackoverflow.com/users/2887218/jcalz
 * @see https://stackoverflow.com/a/50375286/10325032
 */
type UnionToIntersection<Union> =
  (Union extends any
    ? (argument: Union) => void
    : never
  ) extends (argument: infer Intersection) => void
      ? Intersection

karol-majewski

const waitFor = (signal$: Rx.Observable<unknown>) => <T>(source$: Rx.Observable<T>) =>
  Rx.merge(source$.pipe(Rx.buffer(signal$), Rx.mergeAll()), source$.pipe(Rx.skipUntil(signal$)));

karol-majewski

javascript: void function (elements, values, callback) {
  elements.forEach(element => {
    Array.from(element.attributes).forEach(attribute => {
      if (values.includes(attribute.value)) {
        callback(element)
      }
    });
  });
}(
  Array.from(document.querySelectorAll('*')),

karol-majewski

declare class Foo<T, U> {
    a(): string;
}

interface Foo<T extends any[], U> {
    (...args: T): U | Promise<U>;
}

const foo = new Foo<[], void>();
const bar: void | Promise<void> = foo();