How to Handle JSON Requests and Responses in a Node.js Server

How to Handle JSON Requests and Responses in a Node.js Server

JSON is the standard API format. Here is how to handle it in a Node.js server.

Reading JSON Request Bodies

The request body is a stream. For JSON, listen to 'data' for chunks, concatenate, and JSON.parse on 'end'. In Express, use express.json() middleware which does this automatically.

Sending JSON Responses

Set Content-Type to application/json with response.writeHead(200, { 'Content-Type': 'application/json' }), then send JSON.stringify(data) with response.end.

Handling Invalid JSON

If JSON.parse fails, the body is not valid JSON. Catch the error and send a 400 Bad Request response. Express's json middleware does this automatically, returning 400 for invalid JSON.

Large JSON Bodies

For very large JSON, use streaming JSON parsers instead of loading the entire body into memory. This keeps memory low for large payloads.

Content-Type Checking

Check the Content-Type header to confirm it is application/json before parsing as JSON. This prevents errors when the client sends a different format.

The Takeaway

Handle JSON in Node.js by reading the body stream and parsing with JSON.parse, sending responses with Content-Type application/json and JSON.stringify, handling invalid JSON with a 400, using streaming parsers for large bodies, and checking Content-Type. Express's json middleware automates most of this.