1. Middleware Not Executing in Correct Order

Understanding the Issue

Koa.js middleware functions may not execute in the expected order, leading to incorrect application behavior.

Root Causes

• Middleware functions not properly chained using await next().
• Incorrect middleware registration order.
• Using synchronous middleware that blocks execution.

Fix

Ensure that each middleware function calls await next():

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

app.use(async (ctx, next) => {
  console.log("Middleware 1 Start");
  await next();
  console.log("Middleware 1 End");
});

app.use(async (ctx, next) => {
  console.log("Middleware 2");
  await next();
});

Register middleware in the correct sequence:

app.use(loggingMiddleware);
app.use(errorHandlingMiddleware);
app.use(router.routes());

2. Error Handling Not Working

Understanding the Issue

Unhandled errors may crash the application or return unstructured responses.

Root Causes

• Lack of a global error-handling middleware.
• Errors thrown outside of async functions are not caught.
• Improper usage of ctx.throw() and try/catch.

Fix

Use a centralized error-handling middleware:

app.use(async (ctx, next) => {
  try {
    await next();
  } catch (err) {
    ctx.status = err.status || 500;
    ctx.body = { error: err.message };
  }
});

Ensure ctx.throw() is used properly:

if (!user) {
  ctx.throw(404, "User not found");
}

3. Request Body Not Parsing Correctly

Understanding the Issue

Request bodies may not be accessible in route handlers.

Root Causes

• Missing body-parsing middleware.
• Incorrect Content-Type header in requests.
• Parsing large payloads without increasing request limits.

Fix

Install and use koa-bodyparser:

const bodyParser = require("koa-bodyparser");
app.use(bodyParser());

Ensure the correct Content-Type header is set in requests:

fetch("/api", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ key: "value" })
});

4. Routing Not Working

Understanding the Issue

Routes may not be recognized, leading to 404 errors.

Root Causes

• Router middleware not registered properly.
• Incorrect HTTP methods or paths in route definitions.
• Order of middleware execution preventing route handling.

Fix

Use koa-router and register it correctly:

const Router = require("koa-router");
const router = new Router();

router.get("/hello", async (ctx) => {
  ctx.body = "Hello, world!";
});

app.use(router.routes());
app.use(router.allowedMethods());

Ensure HTTP method matches the request:

fetch("/hello", { method: "GET" })

5. Performance Bottlenecks

Understanding the Issue

Koa applications may become slow under heavy load.

Root Causes

• Blocking synchronous operations in middleware.
• Unoptimized database queries slowing down requests.
• Excessive logging and debugging affecting response times.

Fix

Ensure all operations are asynchronous:

app.use(async (ctx, next) => {
  const data = await fetchFromDatabase();
  ctx.body = data;
  await next();
});

Optimize database queries with indexes and caching:

const cachedData = cache.get("user-data");
if (!cachedData) {
  const data = await db.query("SELECT * FROM users");
  cache.set("user-data", data);
}

Use a logging library with configurable levels:

const logger = require("koa-logger");
app.use(logger());

Conclusion

Koa.js simplifies building server-side applications, but troubleshooting middleware execution, error handling, request parsing, routing issues, and performance bottlenecks is crucial for maintaining a stable and efficient API. By structuring middleware correctly, optimizing database interactions, and using proper debugging techniques, developers can enhance their Koa applications.

FAQs

1. Why is my middleware not executing correctly?

Ensure await next() is called in each middleware function and check execution order.

2. How do I handle errors globally in Koa?

Use a centralized error-handling middleware to catch and format errors.

3. Why is my request body not available in Koa?

Ensure koa-bodyparser is used and verify that the correct Content-Type is sent.

4. How do I fix routing issues in Koa?

Register koa-router correctly and confirm the route matches the request method.

5. How can I improve Koa.js performance?

Avoid blocking operations, optimize database queries, and implement caching.