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