JarCastingternary-stream 
A ternary stream: conditionally control the flow of stream data
Usage
1: Conditionally filter content
Condition
if the condition returns truthy, data is piped to the child stream
var ternaryStream = require('ternary-stream');
var condition = function (data) {
return true;
};
process.stdin
.pipe(ternaryStream(condition, process.stdout))
.pipe(fs.createWriteStream('./out.txt'));
Data will conditionally go to stdout, and always go to the file
2: Ternary stream
Ternary
var ternaryStream = require('ternary-stream');
var through2 = require('through2');
var count = 0;
var condition = function (data) {
count++;
return count % 2;
};
process.stdin
.pipe(ternaryStream(condition, fs.createWriteStream('./truthy.txt'), fs.createWriteStream('./falsey.txt')))
.pipe(process.stdout);
Data will either go to truthy.txt (if condition is true) or falsey.txt (if condition is false) and will always go to stdout
API
ternaryStream(condition, stream [, elseStream])
ternary-stream will pipe data to stream whenever condition is truthy.
If condition is falsey and elseStream is passed, data will pipe to elseStream.
After data is piped to stream or elseStream or neither, data is piped down-stream.
Parameters
condition
Type: function: takes in stream data and returns boolean
function (data) {
return true; // or false
}
stream
Stream for ternary-stream to pipe data into when condition is truthy.
elseStream
Optional, Stream for ternary-stream to pipe data into when condition is falsey.
LICENSE
(MIT License)
Copyright (c) 2014 Richardson & Sons, LLC
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.