How to uglify output with Browserify in Gulp?

You actually got pretty close, except for one thing:

• you need to convert the streaming vinyl file object given by source() with vinyl-buffer because gulp-uglify (and most gulp plugins) works on buffered vinyl file objects

So you’d have this instead

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

gulp.task('browserify', function() {
  return browserify('./source/scripts/app.js')
    .bundle()
    .pipe(source('bundle.js')) // gives streaming vinyl file object
    .pipe(buffer()) // <----- convert from streaming to buffered vinyl file object
    .pipe(uglify()) // now gulp-uglify works 
    .pipe(gulp.dest('./build/scripts'));
});

Or, you can choose to use vinyl-transform instead which takes care of both streaming and buffered vinyl file objects for you, like so

var gulp = require('gulp');
var browserify = require('browserify');
var transform = require('vinyl-transform');
var uglify = require('gulp-uglify');


gulp.task('build', function () {

  // use `vinyl-transform` to wrap the regular ReadableStream returned by `b.bundle();` with vinyl file object
  // so that we can use it down a vinyl pipeline
  // while taking care of both streaming and buffered vinyl file objects
  var browserified = transform(function(filename) {
    // filename="./source/scripts/app.js" in this case
    return browserify(filename)
      .bundle();
  });

  return gulp.src(['./source/scripts/app.js']) // you can also use glob patterns here to browserify->uglify multiple files
    .pipe(browserified)
    .pipe(uglify())
    .pipe(gulp.dest('./build/scripts'));
});

Both of the above recipes will achieve the same thing.

Its just about how you want to manage your pipes (converting between regular NodeJS Streams and streaming vinyl file objects and buffered vinyl file objects)

Edit:
I’ve written a longer article regarding using gulp + browserify and different approaches at: https://medium.com/@sogko/gulp-browserify-the-gulp-y-way-bb359b3f9623