Incremental Npm update when package.json changes

This is a stateful stream. It never ends, because it should keep track of the diffs on package.json.

Make sure to create only one instance of it in your gulpfile.js.

1. The first time it gets a package.json file, it will run an npm install command.
2. Afterwards, it will run install/remove only the new packages.

It can keep track of several package.json files.

The following example invokes an update with the stream.write api, however you can pipe other streams to it as well.

The thing is that most of the streams would end as soon as they done, which will cause gulp-update to end as well.

Simply make sure that the stream the is being piped to gulp-update won't end.

var gulp  = require('gulp');

gulp.task('npmUpdate', function () {
  var update = require('gulp-update)();

  gulp.watch('./package.json').on('change', function (file) {
    update.write(file);
  });

})

gulp.task('default', ['npmUpdate']);

With npm do:

npm install gulp-update

MIT