Dependency Injection in 24 lines of code using Typescript

di.ts

type ObjectType<T> = new (...args: unknown[]) => T;

const C = new Map();

const ascii = (a: string) => a.charCodeAt(0);

const toHashKey = <T>(c: ObjectType<T>) =>
  `${c}`
    .split('')
    .map(ascii)
    .join('')
    .substring(0, 50);

export const get = <T>(c: ObjectType<T>): T => C.get(toHashKey(c));
export const has = <T>(c: ObjectType<T>): boolean => !!C.has(toHashKey(c));
export const set = <T>(c: ObjectType<T>, hash = toHashKey(c)): T =>
  C.set(hash, new c()).get(hash);

export const Inject = <T>(clazz: ObjectType<T>): PropertyDecorator => (
  target,
  name: string
) =>
  Object.defineProperty(target, name, {
    get: () => set(clazz)
  });