Fun is a simple functional web application framework for Deno

How to build web application with Fun

There are 3 steps you need to do.

Define a global context

context represents global values shared by the entire web application, like configuration, database connection. In order to build a robust web application, it’s highly recommended that you initialize those resources before starting the application. It can be any data you need when you run the application.
```
 type Context = {
   database: string,
 }

 const context: Context = {
   database: "postgresql://localhost"
 };
```

Write routes and handlers

route is build with different parser, let’s say you want to build an parser match the request GET /api/v1/users/100 (100 can be any integer), you can write code

 // match http method GET
 const get = method<Context>("GET");

 const apiSegment = literal("api");
 const v1Segment = literal("v1");
 const usersSegment = literal("users");
 // match any segment that can be parsed as an integer
 const userIdSegment = integer();

 // match http path /api/v1/users/{any integer}
 const pathParser = combine([
   apiSegment,
   v1Segment,
   usersSegment,
   userIdSegment,
 ] as const);

 // match query parameter
 const queryParams = query({
   role: equal("admin"),
 });

 // build an route that match GET /api/v1/users/{any integer}
 const paths = [get, path(pathParser), queryParams] as const;

 const userRoute = route<Context, typeof paths>(paths);

userRoute’s type will looks like below

// Route has 3 generic parameters
// 1st one is the type of Context we defined above
// 2nd one is the return value of route parser, in this case
//   type:    [string, [string, string, string, number]]
//   parser:  [get,    [api,    v1,     users,  userId]]
// 3rd one is the return value of query parameter parser, which is { role: string }, or
//   more accurate { role: 'admin' }
const userRoute: Route<Context, [string, [string, string, string, number], { role: string }]>

In order to handle the request that match the type of userRoute, you also need to provide a function which type should match with userRoute

function handler(context: Context, params: [string, [string, string, string, number], { role: string }]>): Response;

For example, you can just return context and params in handler

function handler(context: Context, params: [string, [string, string, string, number]]) {
  const body = {
    method, // GET
    path: [api, v1, users, userId], // ["api", "v1", "users", 100]
    context,
  };
  return new Response(JSON.stringify(body), {
    status: 200,
  });
}

Create an web application and register route & handler

const app = new App<Context>(context);
app.route(userRoute, handler);

app.run({
  port: 8080,
});

Now, you can start run your code and visit http://localhost:8080/api/v1/users/100, the response will be

   {"method":"GET","path":["api","v1","users",100],"queryParams":{"role":"admin"},"context":{"framework":"Fun"}}

Check ./exmple.ts for a complete example.