on-headers

Execute a listener when a response is about to write headers

on-headers

Execute a listener when a response is about to write headers.

$ npm install on-headers
var onHeaders = require('on-headers')

This will add the listener listener to fire when headers are emitted for res. The listener is passed the response object as it's context (this). Headers are considered to be emitted only once, right before they are sent to the client.

When this is called multiple times on the same res, the listeners are fired in the reverse order they were added.

var http = require('http')
var onHeaders = require('on-headers')
 
http
.createServer(onRequest)
.listen(3000)
 
function addPoweredBy() {
  // add if not set by end of request 
  if (!this.getHeader('X-Powered-By')) {
    this.addHeader('X-Powered-By', 'Node.js')
  }
}
 
function onRequest(reqres) {
  onHeaders(res, addPoweredBy)
 
  res.setHeader('Content-Type', 'text/plain')
  res.end('hello!')
}

MIT