| 1 | # on-headers
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| 2 |
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| 3 | [![NPM Version][npm-version-image]][npm-url]
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| 4 | [![NPM Downloads][npm-downloads-image]][npm-url]
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| 5 | [![Node.js Version][node-image]][node-url]
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| 6 | [![Build Status][ci-image]][ci-url]
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| 7 | [![Coverage Status][coveralls-image]][coveralls-url]
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| 8 |
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| 9 | Execute a listener when a response is about to write headers.
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| 10 |
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| 11 | ## Installation
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| 12 |
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| 13 | This is a [Node.js](https://nodejs.org/en/) module available through the
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| 14 | [npm registry](https://www.npmjs.com/). Installation is done using the
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| 15 | [`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):
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| 16 |
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| 17 | ```sh
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| 18 | $ npm install on-headers
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| 19 | ```
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| 20 |
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| 21 | ## API
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| 22 |
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| 23 | <!-- eslint-disable no-unused-vars -->
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| 24 |
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| 25 | ```js
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| 26 | var onHeaders = require('on-headers')
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| 27 | ```
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| 28 |
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| 29 | ### onHeaders(res, listener)
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| 30 |
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| 31 | This will add the listener `listener` to fire when headers are emitted for `res`.
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| 32 | The listener is passed the `response` object as it's context (`this`). Headers are
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| 33 | considered to be emitted only once, right before they are sent to the client.
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| 34 |
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| 35 | When this is called multiple times on the same `res`, the `listener`s are fired
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| 36 | in the reverse order they were added.
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| 37 |
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| 38 | ## Examples
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| 39 |
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| 40 | ```js
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| 41 | var http = require('http')
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| 42 | var onHeaders = require('on-headers')
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| 43 |
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| 44 | http
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| 45 | .createServer(onRequest)
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| 46 | .listen(3000)
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| 47 |
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| 48 | function addPoweredBy () {
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| 49 | // set if not set by end of request
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| 50 | if (!this.getHeader('X-Powered-By')) {
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| 51 | this.setHeader('X-Powered-By', 'Node.js')
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| 52 | }
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| 53 | }
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| 54 |
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| 55 | function onRequest (req, res) {
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| 56 | onHeaders(res, addPoweredBy)
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| 57 |
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| 58 | res.setHeader('Content-Type', 'text/plain')
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| 59 | res.end('hello!')
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| 60 | }
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| 61 | ```
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| 62 |
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| 63 | ## Testing
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| 64 |
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| 65 | ```sh
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| 66 | $ npm test
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| 67 | ```
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| 68 |
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| 69 | ## License
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| 70 |
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| 71 | [MIT](LICENSE)
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| 72 |
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| 73 | [ci-image]: https://badgen.net/github/checks/jshttp/on-headers/master?label=ci
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| 74 | [ci-url]: https://github.com/jshttp/on-headers/actions/workflows/ci.yml
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| 75 | [coveralls-image]: https://badgen.net/coveralls/c/github/jshttp/on-headers/master
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| 76 | [coveralls-url]: https://coveralls.io/r/jshttp/on-headers?branch=master
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| 77 | [node-image]: https://badgen.net/npm/node/on-headers
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| 78 | [node-url]: https://nodejs.org/en/download
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| 79 | [npm-downloads-image]: https://badgen.net/npm/dm/on-headers
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| 80 | [npm-url]: https://npmjs.org/package/on-headers
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| 81 | [npm-version-image]: https://badgen.net/npm/v/on-headers
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