Lint, concatenate and compress JavaScript:

gulpfile.js

var gulp = require('gulp'),
	gutil = require('gulp-util'),
	jshint = require('gulp-jshint'),
	uglify = require('gulp-uglify'),
	concat = require('gulp-concat');
	
gulp.task('js', function() {
	return gulp.src('./source/assets/js/*.js')
		.pipe(jshint())
		.pipe(concat('main.js'))
		.pipe(gutil.env.production ? uglify() : gutil.noop())
		.pipe(gulp.dest('./build/assets/js'));
});