Magento 2 Minification Gulp Script

gulpfile.js

var gulp = require('gulp');
var cleanCSS = require('gulp-clean-css');

var minify = require('gulp-minify');


gulp.task('default', [
	'css',
	'requireJsMinify',
	'jsMinify'
]);

gulp.task('css', function() {
	return gulp.src('./../pub/static/frontend/YourTheme/default/en_GB/**/*.css')
	.pipe(cleanCSS({compatibility: 'ie9', processImport: false}))
	.pipe(gulp.dest('./../pub/static/frontend/YourTheme/default/en_GB/'));
});

gulp.task('requireJsMinify', function() {
	gulp.src('./../pub/static/_requirejs/frontend/YourTheme/default/en_GB/**/*.js')
    .pipe(minify({
	    ext: {
		    min: '.js'
	    },
	    noSource: {}
    }))
    .pipe(gulp.dest('./../pub/static/_requirejs/frontend/YourTheme/default/en_GB/'));
});

gulp.task('jsMinify', function() {
    gulp.src('./../pub/static/frontend/YourTheme/default/en_GB/**/*.js')
    .pipe(minify({
	    ext: {
		    min: '.js'
	    },
	    mangle: false,
	    noSource: {}
    }))
    .pipe(gulp.dest('./../pub/static/frontend/YouTheme/default/en_GB/'));
});