Trai

Typescript-first server framework

Project status

Early development. Not suitable for production use, but feel free to try it out and give feedback.

About trai

Most existing Node.JS server frameworks are designed to be used with untyped Javascript. This means that if you want to add validation, you probably need to add (1) a validation schema, and (2) a Typescript interface that redefines this schema for type checking. Most Typescript solutions for this use the dependency injection pattern and still require rather verbose and often redundant typing.

Trai is a Typescript-first JSON Rest API server framework with two primary goals:

1. A fully typed API that enabled type checking route handlers and logic on compile rather than on runtime
2. An easy to use, explicitly typed API that offers the same feature set as Express.

Use with Javascript

Trai is designed to be used with Typescript. You can use it with regular Javascript as well, but there are probably other solutions out there that are a better fit.

How to use trai

This readme serves as a basic step-by-step tutorial to create a simple server application. You can find the resulting application in the example directory.

Let's start by creating a Typescript project and installing the module.

yarn add trai

Create a server definition file server.ts:

import { createServer } from 'trai';

export const server = createServer()
  .enableLogging()
  .findRoutes(__dirname + '/routes')
  .create();

As you can see, trai relies heavily on the builder pattern. This lets the library construct flexible and accurate types.

Create a directory routes next to your server.ts and add your first route in routes/hello.ts:

import { server } from '../server';

server.route('GET', '/hello/:name')
  .param('name')
  .handle(async ctx => {
    return {
      hello: ctx.params.name,
    };
  });

Lastly, create your application's entrypoint and start the server in index.ts:

import { server } from './server';

async function main() {
  let port = 8080;
  await server.start(port);
}

main();

When you build and run the application, your server will automatically import every module from the routes directory, so you don't need to import those routes manually. And because the routes extend from the server, they automatically inherit the correct types from any plugins and middleware you define. Speaking of which...

Middleware

A middleware is a function that gets executed on each request, before a route handler is invoked. Middleware can extend the current request context with additional data. You can use this for a lot of things: cookie parsing, user authentication, etc...

Let's create a user middleware in middleware/user.ts:

import { createMiddleware } from 'trai';

export const userMiddleware = createMiddleware()
  .handle(async ctx => {
    return {
      user: {
        role: 'admin',
      }
    };
  });

Next, add it to our server in server.ts:

import { createServer } from 'trai';
import { userMiddleware } from './middleware/user';

export const server = createServer()
  .enableLogging()
  .findRoutes(__dirname + '/routes')
  .middleware(userMiddleware) // <== Add your middleware
  .create();

And add a new route to view our user info in routes/user.ts:

import { server } from '../server';

server.route('GET', '/user')
  .handle(async ctx => {
    return {
      user: ctx.user,
    };
  });

If you're using an IDE with autocomplete/intellisense, you'll notice that it knows all about the user property on ctx now that you've added the middleware to the server.

Guards

A route guard is a middleware function that doesn't add to a request, but only indicates whether or not a request is valid. It receives the request context and simply returns true or false, indicating whether the request should be handled or not.

Middlewares and guards will run in the order they are defined, so you can use the data from an earlier middleware in a route guard.

Let's use our previously created userMiddleware and create a route guard to limit access to a special admin route. First, create a guard in guards/isAdmin.ts:

import { createGuard } from 'trai';

export const isAdmin = createGuard()
  .handle(async ctx => {
    return ctx.user.role === 'admin';
  });

You'll notice that Typescript throws an error here. Since this guard doesn't extend from the server, it doesn't know about the user property that the userMiddleware adds. So we'll need to explicitly specify what properties we expect ctx to have, by adding a generic type to the createGuard function:

import { createGuard } from 'trai';

export const isAdmin = createGuard<{ user : { role : string } }>()
  .handle(async ctx => {
    return ctx.user.role === 'admin';
  });

Now we'll only be able to add this guard to routes that have a user property on their ctx that conforms to the generic signature we added.

This generics-based approach allows anyone to make and publish middleware, guards and plugins for trai while maintaining strict type checking.

Guards can't be set directly on the server, only on routes or routers (see below). So let's create an admin route with our new guard in routes/admin.ts:

import { server } from '../server';
import { isAdmin } from '../guards/isAdmin';

server.route('GET', '/admin')
  .guard(isAdmin)
  .handle(async ctx => {
    return {
      status: 'you are an admin',
    };
  });

When you visit the /admin route, you'll see the status message being returned. However, watch what happens if you change the role to anything else in your middleware...

Plugins

A plugin is a function that gets executed once, before the server starts. It has access to the main server object and it can add global data that will be added to every request. You can use a plugin for things like creating a database pool that is accessible from every route handler.

Let's create a plugin to add a users map to each request in plugins/users.ts:

import { createPlugin } from 'trai';

export const usersPlugin = createPlugin(async server => {
	let users = new Map<number, { role : string }>();

	users.set(1, { role: 'admin' });
	users.set(2, { role: 'user' });

	return { users };
});

Then add the plugin to the server:

import { createServer } from 'trai';
import { userMiddleware } from './middleware/user';
import { usersPlugin } from './plugins/users';

export const server = createServer()
  .enableLogging()
  .findRoutes(__dirname + '/routes')
  .plugin(usersPlugin) // <== Add the plugin
  .middleware(userMiddleware)
  .create();

Now every request, middleware and guard will have access to the users map through ctx.users.

Like guards and middleware, plugins are executed in the order they are defined, but they are executed only once when the server is started.

Now that we have the plugin, we can update our middleware to load the users from ctx.users:

import { createMiddleware } from 'trai';

export const userMiddleware = createMiddleware()
  .handle(async ctx => {
    return {
      user: ctx.users.get(1)!,
    };
  });

Our middleware has the same problem as our guard earlier: it doesn't know about the properties set by other plugins and middleware. The solution is the same:

import { createMiddleware } from 'trai';

export const userMiddleware = createMiddleware<{ users : Map<number, { role : string }> }>()
  .handle(async ctx => {
    return {
      user: ctx.users.get(1)!,
    };
  });

Routers

If you have a lot of nested routes, you may want to organise those routes by using a router. This lets you define guards and middleware for a collection of routes, and it lets you easily add a prefix to all nested routes.

Let's create an admin router for all our admin routes. Move routes/admin.ts to /routes/admin/admin.ts and create a new router in routes/adminRouter.ts:

import { server } from '../server';
import { isAdmin } from '../guards/isAdmin';

export const adminRouter = server.router()
  .prefix('/admin')
  .guard(isAdmin)
  .create();

Now we can update our route to use the router and remove the guard in routes/admin/admin.ts:

import { adminRouter } from '../adminRouter';

adminRouter.route('GET', '/admin')
	.handle(async ctx => {
		return {
			status: 'you are an admin',
		};
	});

That covers most of the functionality currently in trai.

If you notice any errors or mistakes in this readme, be sure to file an issue.