compose TypeScript 增强版

compose.ts

/**
 * @module compose
 */

export type Next<C> = (context: C) => Promise<C>;

export type Middleware<C> = (context: C, next: Next<C>) => Promise<C> | C;

export type ComposedMiddleware<C> = (context: C, next?: Next<C>) => Promise<C>;

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

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

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