A gulpfile to compile SASS, add necessary prefixes and minify the resulting css file. Also includes a function to compress images.

gulpfile.js

// Gulp components

const {
    series,
    src,
    dest,
    watch
} = require('gulp');

// Dependencies

const sass = require('gulp-sass');

const plumber = require('gulp-plumber');

const notify = require('gulp-notify');

const browserSync = require('browser-sync').create();

const autoprefixer = require('gulp-autoprefixer');

const cssmin = require('gulp-cssnano');

const imagemin = require('gulp-imagemin');

const imageminJpegRecompress = require('imagemin-jpeg-recompress');

const imageminPngquant = require('imagemin-pngquant');

const newer = require('gulp-newer');

// Function to display a pop-up with errors

function customPlumber(errTitle) {
    return plumber({
        errorHandler: notify.onError({
            // Customizing error title
            title: errTitle || "Error running Gulp",
            message: "Error: <%= error.message %>",
            sound: "Glass"
        })
    });
}

function compileSASS(cb) {
    return src('./scss/**/*.scss').pipe(customPlumber('Error running SASS')).pipe(sass()).pipe(autoprefixer({
        browsers: ['last 2 versions'],
        cascade: false
    })).pipe(cssmin()).pipe(dest('./')).pipe(browserSync.stream());
}

exports.default = function(cb) {
    browserSync.init();
    watch('./scss/*.scss', compileSASS);
    watch('./**/*.php', function(cb) {
        browserSync.reload();
        cb();
    });
    cb();
};

exports.compressImages = function(cb) {
    return src(['img/raw/*.jpg','img/raw/*.png','img/raw/*.jpeg'])
    .pipe(newer('img/'))
    .pipe(imagemin([
        imageminJpegRecompress({
            quality: 'low'
        }),
        imageminPngquant()
    ])).pipe(dest('img/'));
}