getProp.ts

function getProp<T, K extends keyof T>(obj: T, key: K): T[K] {
  return obj[key];
}
  
const obj = { text: 'hello', count: 42 };

let s = getProp(obj, 'text');  // string
let n = getProp(obj, 'count'); // number
let x = getProp(obj, 'foo');   // error

tsTypes.ts

type ObjectType = { x: T, y: U };
type UnionType = T | U;
type IntersectionType = T & U;
type IndexType = keyof T;
type LookupType = T[K];
type MappedType = { [P in K]: X }
type ConditionalType = T extends U ? X : Y;

typestuff.ts

// type Message<T> = Parameters<methods.associateVisitor>;
type func = (...args: any[]) => any;
type Unionize<T> = T[keyof T]
type returns = ReturnType<typeof methods.associateVisitor>;

// type ParameterTypes<T extends {[index: string]: (...args: any[]) => any}> = {
//   [P in keyof T]: Parameters<T[P]>
// };
function somefunc(...args) {
  console.log(args);
}
type Parameters2<T extends (...args: any[]) => any> = T extends (...args: infer P) => any ? P : never;
type UnionToIntersection<U> = (U extends any ? (k: U)=>void : never) extends ((k: infer I)=>void) ? I : never
type PickAndFlatten<T, K extends keyof T> = UnionToIntersection<T[K]>

type GetArgumentType<original extends Function> =
  original extends (...x: infer argumentsType) => any ? argumentsType[0] : never

type Unboxed<T> = T extends (infer U)[] ? U : T;

type Keys<T> = keyof T;
type UnionizeProperties<T extends object> = T[Keys<T>]

type ParameterTypes<T extends {[index: string]: (...args: Array<unknown>) => unknown}> = Parameters<T[keyof T]>
type Methods = typeof methods;

type Message = ParameterTypes<typeof methods>;

type test1 = Parameters<Methods[keyof Methods]>
type test2 = Parameters<typeof methods.associateVisitor>[0]
type test3 = UnionToIntersection<Message>
type test4 = Unboxed<Message>
type test5 = Extract<Message, []>
type test6 = Message['PauseMessage']

type moduleToInterface<T extends {[index: string]: (...args: Array<unknown>) => unknown}> = {
  [P in keyof T]: Parameters<T[P]>[0]
}
type test8 = moduleToInterface<Methods>
type test9 = UnionizeProperties<test8>