stream-reduce Like Array.prototype.reduce but for streams. Given a sync reduce function and an initial value it will return a through stream that emits a single data event with the reduced value once the input stream ends. Example var reduce = require("stream-reduce"); process.stdin.pipe(reduce(function(acc, data) { return acc + data.length;}, 0)).on("data", function(length) { console.log("stdin size:", length);}); Installation npm install stream-reduce