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Contents
# on-headers
[](https://www.npmjs.org/package/on-headers)
[](http://nodejs.org/download/)
[](https://travis-ci.org/jshttp/on-headers)
[](https://coveralls.io/r/jshttp/on-headers)
[](https://www.gittip.com/dougwilson/)
Execute a listener when a response is about to write headers.
## Install
```sh
$ npm install on-headers
```
## API
```js
var onHeaders = require('on-headers')
```
### onHeaders(res, listener)
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 `listener`s are fired
in the reverse order they were added.
## Examples
```js
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(req, res) {
onHeaders(res, addPoweredBy)
res.setHeader('Content-Type', 'text/plain')
res.end('hello!')
}
```
## License
[MIT](LICENSE)
Version data entries
17 entries across 17 versions & 2 rubygems