How to Send JSON Response in Oak Framework for Deno

In Oak for Deno, send a JSON response by setting ctx.response.body to a JavaScript object. Oak automatically converts it to JSON and sets the correct Content-Type header.

Syntax

To send a JSON response in Oak, assign a JavaScript object or array to ctx.response.body. Oak handles serialization and headers automatically.

Parts explained:

• ctx: The context object representing the HTTP request and response.
• response: The response part of the context.
• body: The property where you set the response content.

typescript

ctx.response.body = { message: "Hello, world!" };

Example

This example shows a simple Oak server that responds with JSON when you visit the root URL.

typescript

import { Application, Router } from "https://deno.land/x/oak@v12.5.0/mod.ts";

const router = new Router();

router.get("/", (ctx) => {
  ctx.response.body = { greeting: "Hello from Oak!" };
});

const app = new Application();
app.use(router.routes());
app.use(router.allowedMethods());

console.log("Server running on http://localhost:8000");
await app.listen({ port: 8000 });

Output

Server running on http://localhost:8000

Common Pitfalls

Some common mistakes when sending JSON responses in Oak include:

• Setting ctx.response.body to a stringified JSON instead of an object, which causes Oak to send plain text instead of JSON.
• Not setting the response body at all, resulting in empty responses.
• Manually setting Content-Type header incorrectly; Oak sets it automatically when you assign an object.

typescript

/* Wrong way: sending string instead of object */
ctx.response.body = JSON.stringify({ error: "Not found" });
ctx.response.type = "application/json"; // manual header

/* Right way: assign object directly */
ctx.response.body = { error: "Not found" };

Quick Reference

Summary tips for sending JSON in Oak:

• Assign JavaScript objects or arrays directly to ctx.response.body.
• Do not stringify the object yourself.
• Oak sets Content-Type: application/json automatically.
• Use ctx.response.status to set HTTP status codes if needed.

Key Takeaways

Set ctx.response.body to a JavaScript object to send JSON in Oak.

Do not manually stringify JSON; Oak handles it automatically.

Oak sets the Content-Type header to application/json when body is an object.

Use ctx.response.status to control HTTP status codes with JSON responses.