koa-compose TypeScript 实现

koa-compose.ts

/**
 * @module compose
 */

export interface Next {
  (): Promise<void>;
}

export interface Composed<C> {
  (context: C, next?: Next): Promise<void>;
}

export interface Middleware<C> {
  (context: C, next: Next): Promise<void> | void;
}


/**
 * @function compose
 * @description compose koa middlewares
 * @param {function[]} middlewares
 * @returns {function}
 */
export default function compose<C>(middlewares: Middleware<C>[]): Composed<C> {
  const done = async (): Promise<void> => {};

  const compose = middlewares.reduce((compose, middleware) => {
    return (context, next) => {
      return compose(context, async () => {
        middleware(context, next);
      });
    };
  });

  return async (context, next = done) => {
    return compose ? compose(context, next) : next();
  };
}