Nodejs how to set content-type header for every request

To update the request headers please add below custom middleware before bodyparser

app.use(function (req, res, next) {
  req.headers['content-type'] = 'application/json';
  next();
});

If still not working check the case of 'content-type' sent by your client. Put the 'content-type' in the same case

Response object has to use .setHeader instead of .header:

app.use(function(req, res, next) {
    res.setHeader("Content-Type", "application/json");
    next();
});

doc.

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