63 lines
1.5 KiB
Markdown
63 lines
1.5 KiB
Markdown
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# first-chunk-stream [](https://travis-ci.org/sindresorhus/first-chunk-stream)
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> Transform the first chunk in a stream
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Useful if you want to do something to the first chunk.
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You can also set the minimum size of that chunk.
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## Install
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```sh
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$ npm install --save first-chunk-stream
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```
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## Usage
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```js
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var fs = require('fs');
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var concat = require('concat-stream');
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var firstChunk = require('first-chunk-stream');
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// unicorn.txt => unicorn rainbow
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// `highWaterMark: 1` means it will only read 1 byte at the time
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fs.createReadStream('unicorn.txt', {highWaterMark: 1})
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.pipe(firstChunk({minSize: 7}, function (chunk, enc, cb) {
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this.push(chunk.toUpperCase());
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cb();
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}))
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.pipe(concat(function (data) {
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console.log(data);
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//=> UNICORN rainbow
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}));
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```
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## API
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### firstChunk([options], transform)
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#### options.minSize
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Type: `number`
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The minimum size of the first chunk.
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#### transform(chunk, encoding, callback)
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*Required*
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Type: `function`
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The [function](http://nodejs.org/docs/latest/api/stream.html#stream_transform_transform_chunk_encoding_callback) that gets the first chunk.
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### firstChunk.ctor()
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Instead of returning a [stream.Transform](http://nodejs.org/docs/latest/api/stream.html#stream_class_stream_transform_1) instance, `firstChunk.ctor()` returns a constructor for a custom Transform. This is useful when you want to use the same transform logic in multiple instances.
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## License
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MIT © [Sindre Sorhus](http://sindresorhus.com)
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