browserify multiple bundles with gulp / vinyl-source-stream

common.js

module.exports = "common utils";

foo.js

var common = require('./common');

//... do something with common utils

module.exports = "foo";

gulpfile.js

var gulp = require('gulp');
var browserify = require('browserify');
var source = require('vinyl-source-stream');

gulp.task('browserify-common', function() {
  var bundleStream = browserify('./common.js')
        .require('./common.js') //allows you to require('./common')
        .bundle();

  bundleStream
    .pipe(source('./common.js'))
    .pipe(gulp.dest('./bin'));
})

gulp.task('browserify-main', function() {
  var bundleStream = browserify('./index.js')
        .external('./common.js') //don't bundle in the common libs
        //.. add more external libs if necessary
        .bundle()

  bundleStream
    .pipe(source('./index.js'))
    .pipe(gulp.dest('./bin'))
})

index.js

//our entry point...

var foo = require('./foo');
var common = require('./common');

console.log("foo", foo);
console.log("common", common);