gulp/docs/recipes/combining-streams-to-handle-errors.md

The streaming build system

# Combining streams to handle errors #

By default, emitting an error on a stream will cause it to be thrown
unless it already has a listener attached to the `error` event. This
gets a bit tricky when you're working with longer pipelines of streams.

By using [gulp-util](https://github.com/gulpjs/gulp-util)'s `combine`
method you can turn a series of streams into a single stream, meaning you
only need to listen to the `error` event in one place in your code.

Here's an example of using it in a gulpfile:

``` javascript
var combine = require('gulp-util').combine
var uglify = require('gulp-uglify')
var gulp = require('gulp')

gulp.task('test', function() {
  var combined = combine(
    gulp.src('bootstrap/js/*.js'),
    uglify(),
    gulp.dest('public/bootstrap')
  )

  // any errors in the above streams
  // will get caught by this listener,
  // instead of being thrown:
  combined.on('error', function(err) {
    console.warn(err.message)
  })

  return combined
})
```

You can use this technique in your gulp plugins and node modules too using
the [multipipe](http://npmjs.org/package/multipipe) module, and is a generally useful means of ensuring that errors aren't thrown from inaccessible streams
somewhere deep inside `./node_modules`.