villa/src/function.ts

Promise utilities for async/await-ready environment.

import {NodeStyleCallback} from '.';

export type NodeStyleAsyncFunction<T> =
  | ((callback: NodeStyleCallback<T>) => any)
  | ((arg0: any, callback: NodeStyleCallback<T>) => any)
  | ((arg0: any, arg1: any, callback: NodeStyleCallback<T>) => any)
  | ((arg0: any, arg1: any, arg2: any, callback: NodeStyleCallback<T>) => any)
  | ((
      arg0: any,
      arg1: any,
      arg2: any,
      arg3: any,
      callback: NodeStyleCallback<T>,
    ) => any)
  | Function;

/**
 * Call a Node.js-style asynchronous function and return a correspondent
 * promise.
 */
export function call<T>(
  fn: NodeStyleAsyncFunction<T>,
  ...args: any[]
): Promise<T> {
  return new Promise<T>((resolve, reject) => {
    fn.call(undefined, ...args, (error: any, value: T) => {
      if (error) {
        reject(error);
      } else {
        resolve(value);
      }
    });
  });
}

export type AsyncFunction<T> = (...args: any[]) => Promise<T>;

/**
 * Wrap a Node.js-style asynchronous function to a function that returns
 * promise.
 */
export function async<T>(fn: NodeStyleAsyncFunction<T>): AsyncFunction<T> {
  return function(this: any, ...args: any[]): Promise<T> {
    return new Promise<T>((resolve, reject) => {
      fn.call(this, ...args, (error: any, value: T) => {
        if (error) {
          reject(error);
        } else {
          resolve(value);
        }
      });
    });
  };
}