How to write an async middleware in koa?

@lizzie 

To write an async middleware in Koa, you can use the async/await syntax provided by JavaScript. Here is an example of how you can create an async middleware in Koa:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

const Koa = require('koa');
const app = new Koa();

// Async middleware function
const asyncMiddleware = async (ctx, next) => {
  // Do asynchronous operations here
  await someAsyncFunction();

  // Call the next middleware in the chain
  await next();
};

// Use the async middleware in your Koa app
app.use(asyncMiddleware);

// Example route
app.use(ctx => {
  ctx.body = 'Hello World';
});

// Start the server
app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

In the example above, we define an async middleware function asyncMiddleware that performs some asynchronous operation using await. Inside the async middleware, we use await next() to call the next middleware in the chain.

Then, we register the async middleware using app.use(asyncMiddleware). Finally, we define a simple route handler using app.use(ctx => {}) to respond with 'Hello World'.

When you run the Koa app, the async middleware will be executed before the route handler, allowing you to perform asynchronous operations before responding to the client.