serviejs / throwback

An asynchronous middleware pattern

Throwback

Simple asynchronous middleware pattern.

Installation

npm install throwback --save

Usage

Compose asynchronous (promise-returning) functions.

const { compose } = require("throwback");

const fn = compose([
  async function(ctx, next) {
    console.log(1);

    try {
      await next();
    } catch (err) {
      console.log("throwback", err);
    }

    console.log(4);
  },
  async function(ctx, next) {
    console.log(2);

    return next();
  }
]);

// Callback runs at the end of the stack, before
// the middleware bubbles back to the beginning.
fn({}, function(ctx) {
  console.log(3);

  ctx.status = 404;
});

Tip: In development (NODE_ENV !== "production"), compose will throw errors when you do something unexpected. In production, the faster non-error code paths are used.

Example

Build a micro HTTP server!

const { createServer } = require("http");
const finalhandler = require("finalhandler"); // Example only, not compatible with single `ctx` arg.
const { compose } = require("throwback");

const app = compose([
  function({ req, res }, next) {
    res.end("Hello world!");
  }
]);

createServer(function(req, res) {
  return app({ req, res }, finalhandler());
}).listen(3000);

Use Cases

• HTTP requests (e.g. popsicle)
• HTTP servers (e.g. servie)
• Processing pipelines (e.g. scrappy)

Inspiration

Built for servie and inspired by koa-compose.

License

MIT