1 | # from2 [![Flattr this!](https://api.flattr.com/button/flattr-badge-large.png)](https://flattr.com/submit/auto?user_id=hughskennedy&url=http://github.com/hughsk/from2&title=from2&description=hughsk/from2%20on%20GitHub&language=en_GB&tags=flattr,github,javascript&category=software)[![experimental](http://hughsk.github.io/stability-badges/dist/experimental.svg)](http://github.com/hughsk/stability-badges) #
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2 |
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3 | `from2` is a high-level module for creating readable streams that properly handle backpressure.
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4 |
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5 | Convience wrapper for
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6 | [readable-stream](http://github.com/isaacs/readable-stream)'s `ReadableStream`
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7 | base class, with an API lifted from
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8 | [from](http://github.com/dominictarr/from) and
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9 | [through2](http://github.com/rvagg/through2).
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10 |
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11 | ## Usage ##
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12 |
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13 | [![from2](https://nodei.co/npm/from2.png?mini=true)](https://nodei.co/npm/from2)
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14 |
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15 | ### `stream = from2([opts], read)` ###
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16 |
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17 | Where `opts` are the options to pass on to the `ReadableStream` constructor,
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18 | and `read(size, next)` is called when data is requested from the stream.
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19 |
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20 | * `size` is the recommended amount of data (in bytes) to retrieve.
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21 | * `next(err)` should be called when you're ready to emit more data.
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22 |
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23 | For example, here's a readable stream that emits the contents of a given
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24 | string:
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25 |
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26 | ``` javascript
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27 | var from = require('from2')
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28 |
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29 | function fromString(string) {
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30 | return from(function(size, next) {
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31 | // if there's no more content
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32 | // left in the string, close the stream.
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33 | if (string.length <= 0) return next(null, null)
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34 |
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35 | // Pull in a new chunk of text,
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36 | // removing it from the string.
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37 | var chunk = string.slice(0, size)
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38 | string = string.slice(size)
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39 |
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40 | // Emit "chunk" from the stream.
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41 | next(null, chunk)
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42 | })
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43 | }
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44 |
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45 | // pipe "hello world" out
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46 | // to stdout.
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47 | fromString('hello world').pipe(process.stdout)
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48 | ```
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49 |
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50 | ### `stream = from2.obj([opts], read)` ###
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51 |
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52 | Shorthand for `from2({ objectMode: true }, read)`.
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53 |
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54 | ### `createStream = from2.ctor([opts], read)` ###
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55 |
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56 | If you're creating similar streams in quick succession you can improve
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57 | performance by generating a stream **constructor** that you can reuse instead
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58 | of creating one-off streams on each call.
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59 |
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60 | Takes the same options as `from2`, instead returning a constructor which you
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61 | can use to create new streams.
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62 |
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63 | ### See Also
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64 |
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65 | - [from2-array](https://github.com/binocarlos/from2-array) - Create a from2 stream based on an array of source values.
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66 | - [from2-string](https://github.com/yoshuawuyts/from2-string) - Create a stream from a string. Sugary wrapper around from2.
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67 |
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68 | ## License ##
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69 |
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70 | MIT. See [LICENSE.md](http://github.com/hughsk/from2/blob/master/LICENSE.md) for details.
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