dldc-packages/compose

🏯 A middleware and context system

🏯 Miid

A type-safe middleware system

Example

import { compose, createKey, Stack } from "miid";

const ACtx = createKey<string>({ name: "ACtx", defaultValue: "A" });

const mid = compose<Stack, string>(
  (ctx, next) => {
    console.log("middleware 1");
    console.log(ctx.debug());
    return next(ctx.with(ACtx.Provider("a1")));
  },
  (ctx, next) => {
    console.log("middleware 2");
    console.log(ctx.debug());
    return next(ctx.with(ACtx.Provider("a2")));
  },
  (ctx, next) => {
    console.log("middleware 3");
    console.log(ctx.get(ACtx.Consumer));
    console.log(ctx.debug());
    return next(ctx.with(ACtx.Provider("a3")));
  },
);
const mid2 = compose(mid, (ctx, next) => {
  console.log("done");
  console.log(ctx.debug());
  return next(ctx);
});
mid2(new Stack(), () => {
  console.log("done 2");
  return "nope2";
});

Installation

npm install miid
# or
yarn add miid

Extending Stack

You can create your own Stack:

class CustomStack extends Stack {
  // You need to override the `with` method to return a new instance of your CustomStack
  with(...keys: Array<KeyProvider<any>>): CustomStack {
    // Use the static `applyKeys` method to apply keys to the current instance
    return Stack.applyKeys<CustomStack>(
      this,
      keys,
      (internal) => new CustomStack(internal),
    );
  }
}

const custom = new CustomStack();
expect(custom instanceof CustomStack).toBe(true);
expect(custom instanceof Stack).toBe(true);

If you want to pass custom arguments to yout CustomStack you need to override the withInternal method:

class ParamsStack extends Stack {
  // You can pass your own parameters to the constructor
  constructor(
    public readonly param: string,
    internal: StackInternal<ParamsStack> | null = null,
  ) {
    super(internal);
  }

  with(...keys: Array<KeyProvider<any>>): ParamsStack {
    return Stack.applyKeys<ParamsStack>(
      this,
      keys,
      (internal) => new ParamsStack(this.param, internal),
    );
  }
}

const custom = new ParamsStack("some value");
expect(custom.param).toBe("some value");
expect(custom instanceof ParamsStack).toBe(true);
expect(custom instanceof Stack).toBe(true);