Asynchronising functional programming pattern example

async.ts

type Fn = (...args: any[]) => any;

function makeAsync<T extends Fn>(fn: Fn): (...args: Parameters<T>) => Promise<ReturnType<T>> {
  return function (this: any, ...args: Parameters<T>): Promise<ReturnType<T>> {
    return new Promise<ReturnType<T>>((res, rej) => {
      try {
        res(fn.call(this, ...args));
      } catch (e) {
        rej(e);
      }
    })
  }
}

asynchronising.js

function makeAsync(fn) {
  return function (...args) {
    return new Promise((res, rej) => {
      try {
        res(fn.call(this, ...args));
      } catch (e) {
        rej(e);
      }
    })
  }
}

// it can be used like this
const obj = {
  value: 1,
  add: makeAsync(
    function (a) {
      return this.value + a;
    }
  )
}
obj.add(2).then(r => console.log(r));