Browserify task

gulpfile.js

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

gulp.task('setWatch', function() {
  global.isWatching = true;
});

gulp.task('browserify', function() {
  var bundleMethod = global.isWatching ? watchify : browserify;
  
  var bundler = bundleMethod({
    entries: ['./src/js/app.coffee'],
    extensions: ['coffee']
  });
  
  var bundle = function() {
    return bundler
      .bundle({debug: true})
      .pipe(source('app.js'))
      .pipe(gulp.dest('./build/'))
  };
  
  if(global.isWatching) {
    bundle.on('update', bundle);
  }
  
  return bundle();
});

gulp.task('watch',  ['setWatch', 'browserify'], function() {
  // ...
});

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