code:

var gulp = require('gulp')
var concat = require('gulp-concat')
var uglify = require('gulp-uglify');
var bowerMain = require('bower-main');

var bowerMainJavaScriptFiles = bowerMain('js', 'min.js');

gulp.task('default', ['bower', 'build']);

gulp.task('bower', function() {
    gulp.src(bowerMainJavaScriptFiles.minified)
        .pipe(gulp.dest('lib'))
});

gulp.task('build', function() {
    gulp.src([
            'lib/*.js',
            'src/*.js'
        ])
        .pipe(concat('whatever.min.js'))
        .pipe(uglify())
        .pipe(gulp.dest('dest'))
});