A small promise-based wrapper for through2, based on RangerMauve's through2-map-promise

npm install --save through2-promise

Some examples:

var through2 = require("through2-promise");
fs.createReadStream('ex.txt')
.pipe(through2(function (chunk) {
    for (var i = 0; i < chunk.length; i++) {
        if (chunk[i] == 97)
            chunk[i] = 122; // swap 'a' for 'z'

        this.push(chunk);
    }
}))
.pipe(fs.createWriteStream('out.txt'))
.on('finish', function () {
    doSomethingSpecial()
});

Or object streams:

var all = []

fs.createReadStream('data.csv')
.pipe(csv2())
.pipe(through2.obj(function (chunk) {
    var data = {
        name    : chunk[0],
        address : chunk[3],
        phone   : chunk[10]
    };
    this.push(data);
}))
.on('data', function (data) {
    all.push(data)
})
.on('end', function () {
    doSomethingSpecial(all)
});

Creates a transform stream which calls your transforming function, fn. You can throw within your function to automatically reject the promise and error-out the stream. options is the optional object that gets passed into through2.

this is the through2 stream, so you can do this.push() just like in through2. If you return a Promise, and the Promise resolves to a value, this value will be written to the stream (just like passing a value to the callback in through2).

flushFunction() is a function that runs after the source stream has been consumed. It has access to this.push(), and also any value returned will be appended to the written results.

Same as the former, but the stream is created in objectMode.

Creates a constructor for your transform stream in case you want to be more efficient.