# Response headers in test server in JavaScript

Our server is able to send different HTTP headers. For this, the second parameter of a callback is used:

`export default { '/handler/': function(data, resp) { // resp parameter for headers } }`

Using the `setHeader` method, we can set any header. For example, let's set the MIME type to JSON:

`export default { '/handler/': function(data, resp) { resp.setHeader('Content-Type', 'application/json'); return '[1,2,3]'; } }`

Set the `Content-Type` header to `text/plain`.

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