merge-stream

What is merge-stream?

The merge-stream npm package is used to create a stream that emits events from multiple other streams. This is useful when you want to handle multiple streams as if they were a single stream, for example, when you are dealing with multiple sources of data or tasks in a build process.

What are merge-stream's main functionalities?

Merging multiple streams

This feature allows you to merge multiple streams into one. In the code sample, `stream1` and `stream2` are merged into `mergedStream`. You can then listen to events from `mergedStream` as if it was a single stream.

var stream1 = source1.pipe(transform1);
var stream2 = source2.pipe(transform2);
var mergedStream = mergeStream(stream1, stream2);
mergedStream.on('data', function(data) {
  console.log(data);
});

Adding streams dynamically

This feature allows you to add streams to the merged stream dynamically. Initially, `mergedStream` is created without any sources. Streams `stream1` and `stream2` are then created and added to `mergedStream` dynamically.

var mergedStream = mergeStream();

var stream1 = source1.pipe(transform1);
mergedStream.add(stream1);

var stream2 = source2.pipe(transform2);
mergedStream.add(stream2);

Other packages similar to merge-stream

multistream

Similar to merge-stream, multistream allows you to combine multiple streams into one. However, multistream works by taking an array of streams or a function that returns a stream, and reads them one after the other, not necessarily in parallel as merge-stream does.

combined-stream

Combined-stream is another package that is similar to merge-stream. It is used to create a stream that emits data from multiple streams one after the other. It differs from merge-stream in that it does not handle the streams in parallel but sequentially.

pumpify

Pumpify combines streams into a single duplex stream. This is similar to merge-stream in that it deals with multiple streams, but pumpify is more about creating a pipeline of streams where the output of one stream is the input to the next, rather than merging their outputs.

README

merge-stream

Merge (interleave) a bunch of streams.

Synopsis

var stream1 = new Stream();
var stream2 = new Stream();

var merged = mergeStream(stream1, stream2);

var stream3 = new Stream();
merged.add(stream3);
merged.isEmpty();
//=> false

Description

This is adapted from event-stream separated into a new module, using Streams3.

API

mergeStream

Type: function

Merges an arbitrary number of streams. Returns a merged stream.

merged.add

A method to dynamically add more sources to the stream. The argument supplied to add can be either a source or an array of sources.

merged.isEmpty

A method that tells you if the merged stream is empty.

When a stream is "empty" (aka. no sources were added), it could not be returned to a gulp task.

So, we could do something like this:

stream = require('merge-stream')();
// Something like a loop to add some streams to the merge stream
// stream.add(streamA);
// stream.add(streamB);
return stream.isEmpty() ? null : stream;

Gulp example

An example use case for merge-stream is to combine parts of a task in a project's gulpfile.js like this:

const gulp =          require('gulp');
const htmlValidator = require('gulp-w3c-html-validator');
const jsHint =        require('gulp-jshint');
const mergeStream =   require('merge-stream');

function lint() {
  return mergeStream(
    gulp.src('src/*.html')
      .pipe(htmlValidator())
      .pipe(htmlValidator.reporter()),
    gulp.src('src/*.js')
      .pipe(jsHint())
      .pipe(jsHint.reporter())
  );
}
gulp.task('lint', lint);

License

MIT