gulpFile.js

'use strict';
var gulp=require('gulp'),
    sass=require('gulp-sass'),
    browserSync=require('browser-sync'),
    del=require('del'),
    imagemin=require('gulp-imagemin'),
    uglify=require('gulp-uglify'),
    usemin=require('gulp-usemin'),
    rev=require('gulp-rev'),
    cleanCss=require('gulp-clean-css'),
    flatmap=require('gulp-flatmap'),
    htmlmin=require('gulp-htmlmin');



gulp.task('sass',function()
{
    return gulp.src('./css/*.scss')//source of object
    .pipe(sass().on('error',sass.logError))//pipe objects in function
    .pipe(gulp.dest('./css'));//destination
})  ;

gulp.task('sass:watch',function()
{
    gulp.watch('./css/*.scss',['sass']);
    //gulp watch css files and when chnges occur sass run 

});

gulp.task('browser-sync',function()
{
    var files=[
        './*.html',
        './css/*.css',
        './js/*.js',
        './img/*.{png,jpg,gif}'
    ];
    browserSync.init(files,{
        server:{
            baseDir:'./'
        }

    })
})



gulp.task('default',gulp.series('browser-sync',function(){
    gulp.start('sass:watch');
}))

gulp.task('clean',function()
{
    return del(['dist']);
})

gulp.task('copyfonts',function()
    {
       return gulp.src('./node_modules/font-awesome/fonts/**/*.{ttf,woff,eot,svg}*')
        .pipe(gulp.dest('./dist/fonts'))

    }
)

gulp.task('imagemin',function()
{
    return gulp.src("./img/*.{gif,png,jpg}")
    .pipe(imagemin({optimizedLevel:3,progressive:true,interlaced:true}))
    .pipe(gulp.dest('dist/img'))

})

gulp.task('usemin',function(){
    return gulp.src('./*.html')
    .pipe(flatmap(function(stream,file)
    {
        return stream
        .pipe(usemin({
            css:[rev()],
            html:[function(){return htmlmin({collapseWhitespace:true})}],
            js:[uglify(),rev()],
            inlinejs:[uglify()],
            inlinecss:[cleanCss(),'concat']
        }))
    }))
    .pipe(gulp.dest('dist/'))
})


gulp.task('build',gulp.series('clean',gulp.parallel('copyfonts','imagemin','usemin',function(done){done();}

)))