mscolnick

type TypeName<T> =
    T extends string ? "string" :
    T extends number ? "number" :
    T extends boolean ? "boolean" :
    T extends undefined ? "undefined" :
    T extends Function ? "function" :
    "object";

type T0 = TypeName<string>;  // "string"
type T1 = TypeName<"a">;  // "string"

mscolnick

interface Person {
  name: string;
  age: number;
  location: string;
}

type P1 = Person["name"]; // string
type P2 = string[][0]; // string
type P3 = string[]["length"]; // number
type P4 = [string]["length"]; // 1

mscolnick

function fibonacci(num) {
  if (num <= 1) {
    return 1;
  }

  return fibonacci(num - 1) + fibonacci(num - 2);
}

mscolnick

type Plus1<A extends any[]> = [true, ...A];
type Add<A extends any[], B extends any[]> = [...A, ...B];
type Minus1<A extends any[]> = A extends readonly [any?, ...infer U] ? U : [...A];
type Minus2<A extends any[]> = Minus1<Minus1<A>>;

// verify
type D = Plus1<A>; // [true, true, true, true]
type E = Minus1<A>; // [true, true]
type F = Minus2<A>; // [true]

mscolnick

const SectionedListWrapper = styled.div<{ clickable?: boolean; bordered?: boolean }>`
  display: flex;
  flex-direction: column;
  ${padding.b('$8')}

  ${cond.if(
    'clickable',
    css`
      > *:not(:first-child):hover {
        cursor: pointer;