How do I check if a request is JSON in Node.js?
Check the Content-Type header: request.headers['content-type'] should be application/json. If it is not, the client sent a different format and parsing as JSON would fail. This prevents errors from format mismatches.
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More FAQs in How to Handle JSON Requests and Responses in a Node.js Server
The request body is a stream. Listen to 'data' for chunks, concatenate, and JSON.parse on 'end'. In Express, use express.json() middleware which does this automatically.
Set Content-Type to application/json with response.writeHead(200, { 'Content-Type': 'application/json' }), then send JSON.stringify(data) with response.end.
Catch JSON.parse errors and send a 400 Bad Request response. Express's json middleware does this automatically, returning 400 for invalid JSON, so you do not need to handle it manually.
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