Really basic express-like middleware implementation

middleware.js

class Middleware {
  private middlewares = [];
  push(...middlewares) {
    this.middlewares.push.apply(this.middlewares, middlewares);
  }
  run(...args) {
    let i = 0;
    const next = () => {
      if (i < this.middlewares.length) {
        this.middlewares[i++].apply(null, [...args, next]);
      }
    }
    next();
  }
}

// test it out
let m = new Middleware();
m.push(
  (ctx, next) => { 
    console.log(ctx); 
    ctx.a = 1;
    next();
  },
  (ctx, next) => { 
    console.log(ctx); 
    ctx.a = 2;
    next() 
  }
);
m.run({ a: 0 })