60 lines
1.6 KiB
Markdown
60 lines
1.6 KiB
Markdown
# on-headers
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[](https://www.npmjs.org/package/on-headers)
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[](http://nodejs.org/download/)
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[](https://travis-ci.org/jshttp/on-headers)
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[](https://coveralls.io/r/jshttp/on-headers)
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[](https://www.gittip.com/dougwilson/)
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Execute a listener when a response is about to write headers.
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## Install
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```sh
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$ npm install on-headers
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```
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## API
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```js
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var onHeaders = require('on-headers')
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```
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### onHeaders(res, listener)
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This will add the listener `listener` to fire when headers are emitted for `res`.
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The listener is passed the `response` object as it's context (`this`). Headers are
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considered to be emitted only once, right before they are sent to the client.
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When this is called multiple times on the same `res`, the `listener`s are fired
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in the reverse order they were added.
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## Examples
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```js
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var http = require('http')
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var onHeaders = require('on-headers')
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http
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.createServer(onRequest)
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.listen(3000)
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function addPoweredBy() {
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// add if not set by end of request
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if (!this.getHeader('X-Powered-By')) {
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this.addHeader('X-Powered-By', 'Node.js')
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}
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}
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function onRequest(req, res) {
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onHeaders(res, addPoweredBy)
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res.setHeader('Content-Type', 'text/plain')
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res.end('hello!')
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}
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```
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## License
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[MIT](LICENSE)
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