Andarist

// identity mapped type
https://www.typescriptlang.org/play?#code/PTAEEsDsAcFcBcBQ8Ce0CmoDyAjAVqALygDeioFoAZgPY0BcoAzvAE5QDmANOZTgIatGkWAFsc6VogC+iRCGqxIAY3jgakZGkwBJACbpIa1AB4AKgD4ipXhQDaAaQiRQAa3QoaVUGYC6jM0dfGTkFZX4AGwitDFAAZX5RTGJ9Q2MUE1w8CyA
// promisify mapped type
https://www.typescriptlang.org/play?#code/C4TwDgpgBA8gRgKygXigbygMwPbYFxQDOwATgJYB2A5gDRRwCGJBFArgLZwQlQC+AUP1CQoABRLZ2ZQmUwgAPABUAfCnT8omqAG0A0lEpQA1hBDZMURQF0CACgCUKVeMnSISvVeX8BQ8NBcpGUwyCAATNUDpWQV4BG9+MIgAYwAbJmhk7ApiKBIwZIIo4NCwwSyc4CxWYFYSaFR85IA6RhIHQUwauohm4AALCApbWwA3BlTHZFU0DS1x1J97IA
// SatisfyName, get access to ur own key in the callback
https://www.typescriptlang.org/play?#code/PTAEDMFcDsGMBcCWB7aAoeBPADgU1AMoCGSAzuJgHJEC2uAPACoB8oAvKAN5qigDaAaVCJooANa5MycKEYBdAFygAFNFq4lAgJTtWAN2SIAJgG40AXzNojuWABsiAJ3xQ4SVKFIlE5TAHkAIwArW3hqOiZmZWRgpWIyCnCGFi0lA2MrLwT-YNCk5U5QEFBkSHhsMp5QIiVVdR02Vm4q3jU6M15zABoqgNq23AamltARgY7QbostEyA
// provideValue, just pairs of data and callbacks that get *their* data as an argument
https://www.typescript

Andarist

const microtask = () => {}

async function test() {
  queueMicrotask(() => {
    console.log("1");
    queueMicrotask(() => {
      console.log("2");
    });
  });
  await microtask();

Andarist

async function microtask() {
  return Promise.resolve().then(() => {});
}
async function test() {
  queueMicrotask(() => {
    console.log("1");
    queueMicrotask(() => {
      console.log("2");
    });
  });

Andarist

mapped types syntax and intro

https://www.typescriptlang.org/play?#code/C4TwDgpgBA8gRgKygXigbwFBW1AZge3wC4oBnYAJwEsA7AcwBosc4BDCkmgVwFs4IKGAL4YMoSFACSAEwg1gVUAB4AKgD4U6ZtgDaAaSi0oAawgh8uKCoC6JFfuvDR46AGVWPaKhlyFy+AhqGAD0wTgAegD8omLg0AAKFPg8VKRUuCCqGqiYOFD6hjQmZhZWtlAAFACUKBqJyakQqg5BIrES9SlpuFQQ0pqdqemZAUGhEdEYsgDGADbs0NP4NORQFGDTJIPdvdKiSyvAeFzAXBReaxsAdGwU1SFheU-PUFGiuCdnEFfAABZyFQqADdWLMasgNLkcCDZtooOM3kIqkA

a tweet that prompted the idea for the talk

https://twitter.com/kentcdodds/status/1608187990215655424

but since this isn't possible with satisfies (it doesn't participate in inference, in an example like that it only provides contextual types) the answer was to use a function with a reverse mapped type

Andarist

function createLongLastingContext<T>(factory: () => T) {
  const defaultValue = typeof document !== "undefined" ? factory() : null;
  const ctx = React.createContext<T | null>(defaultValue);
  return {
    useContext: () => {
      const value = React.useContext(ctx);
      if (!value) {
        throw new Error("Context not initialized.");
      }
      return value;

Andarist

const createSingleState = () => ({
  initial: "fetch",
  states: {
    fetch: {
      invoke: {
        src: "fetchSmth",
        onDone: {
          target: "done",
          actions: "notifySingleSuccess"
        }

Andarist

// source
524288; // {"basics":["Object"],"composites":["StructuredType","StructuredOrInstantiable","ObjectFlagsType","Narrowable","NotPrimitiveUnion","IncludesMask"]}
// target
8388608; // {"basics":["IndexedAccess"],"composites":["TypeVariable","InstantiableNonPrimitive","Instantiable","StructuredOrInstantiable","Simplifiable","Narrowable","NotPrimitiveUnion","IncludesWildcard"]}

var flags = {
  Any: 1 << 0,
  Unknown: 1 << 1,
  String: 1 << 2,
  Number: 1 << 3,

Andarist

  // Available variables:
  // - Machine
  // - interpret
  // - assign
  // - send
  // - sendParent
  // - spawn
  // - raise
  // - actions

Andarist

Machine(
  {
    context: {
      networkQuality: "good",
    },
    on: {
      REPORT_NETWORK_QUALITY: {
        actions: [
          assign({
            networkQuality: (_, ev) => ev.networkQuality,

Andarist

Machine({
    initial: 'fetching_user',
    states: {
      fetching_user: {
        invoke: {
          src: 'fetchUser',
          onDone: [{
            cond: 'hasUser',
            target: 'fetching_resources'
          }, {