Can't install gulp4 gulp-sass?

Question

css

I've been trying for a month now, please help!

let project_folder = require("path").basename(__dirname);
let source_folder = "src";

let fs = require('fs');

let path = {
    build: {
        html: project_folder + "/",
        css: project_folder + "/css/",
        js: project_folder + "/js/",
        img: project_folder + "/img/",
        fonts: project_folder + "/fonts/",
    },

    src:{
        html: source_folder + "/*.html",
        css: source_folder + "/scss/style.scss",
        js: source_folder + "/js/script.js",
        img: source_folder + "/img/**/*.{jpg,png,svg,gif,ico,webp}",
        fonts: source_folder + "/fonts/*.ttf",
    },
    watch:{
        html: source_folder + "/**/*.html",
        css: source_folder + "/scss/**/*scss",
        js: source_folder + "/js/**/*.js",
        img: source_folder + "/img/**/*.{jpg,png,svg,gif,ico,webp}",
    },
    clean: "./" + project_folder + "/"
}
let {src, dest } = require('gulp'),
gulp = require('gulp'),
browsersync = require("browser-sync"),
fileinclude = require("gulp-file-include"),
scss = require("gulp-sass"),
autoprefixer = require("gulp-autoprefixer"),
group_media = require("gulp-group-css-media-queries"),
clean_css = require("gulp-clean-css"),
rename = require("gulp-rename"),
unglify = require("gulp-uglify-es"),
imagemin = require("gulp-imagemin"),
webp = require("gulp-webp"),
webphtml = require("gulp-webp-html"),
webpcss = require("gulp-webpcss"),
svgSprite = require("gulp-svg-sprite"),
ttf2woff = require("gulp-ttf2woff"),
ttf2woff2 = require("gulp-ttf2woff2"),
fonter = require('gulp-fonter');

function browserSync(params) {
    browsersync.init({
        server: {
            baseDir: "./" + project_folder + "/"
        },
        port: 3000,
        notify: false
    })
}

function html() {
    return src(path.src.html)
    .pipe(fileinclude())
    .pipe(webphtml( ))
    .pipe(dest(path.build.html))
    .pipe(browsersync.stream())
}

function css() {
    return src(path.src.css)
    .pipe(
        scss({
            outputStyle: "expanded"
        })
        )
    .pipe(
        group_media()
        )
    .pipe( 
        autoprefixer({
            overrideBrowserslist: ["last 5 versions"],
            cascade:true
        })
    )
    .pipe(webpcss())
    .pipe(dest(path.build.css))
    .pipe(clean_css())
    .pipe(dest(path.build.css))
    .pipe(browsersync.stream())
}

function js() {
    return src(path.src.js)
    .pipe(fileinclude())
    .pipe(dest(path.build.js))
    .pipe(browsersync.stream())
    .pipe(
        uglify()
        )
    .pipe(
        rename({
        extname: ".min.js"
    }))
    pipe(dest(path.build.js))
}

function images() {
    return src(path.src.img)
    .pipe(
        webp({
            quality: 70
        })
        )
    .pipe(dest(path.build.img))
    .pipe(src(path.src.img))
    .pipe(
        imagemin({
            progressive: true,
            svgoPlugins: [{removeViewBox: false}],
            interlaced:true,
            optimizationLevel: 3 //0 to 7
        })
        )
    .pipe(dest(path.build.img))
    .pipe(browsersync.stream())
}

function fonts(){
    src(path.src.fonts)
    .pipe(ttf2woff())
    .pipe(dest(path.build.fonts));
    return src(path.src.fonts)
    .pipe(ttf2woff2())
    .pipe(dest(path.build.fonts));
};

gulp.task('otf2ttf'), function(){
    return src([source_folder + '/fonts/*.otf'])
    .pipe(fonter({
        formats: ['tff']
    }))
    .pipe(dest(source_folder+ '/fonts/'));
}

gulp.task('svgSprite', function(){
 return gulp.src([source_folder + '/iconsprite/*.svg'])
 .pipe(svgSprite({
    mode: {
        stack: {
            sprite: "../icons/icons.svg",
           example: true
        }
    },
 }
 ))
 .pipe(dest(path.build.img))
})

function fontsStyle(params) {
        let file_content = fs.readFileSync(source_folder + '/scss/fonts.scss');
        if (file_content == '') {
            fs.writeFile(source_folder + '/scss/fonts.scss', '', cb);
            return fs.readdir(path.build.fonts, function (err, items) {
            if (items) {
            let c_fontname;
            for (var i = 0; i < items.length; i++) {
                let fontname = items[i].split('.');
                fontname = fontname[0];
                if (c_fontname != fontname) {
                    fs.appendFile(source_folder + '/scss/fonts.scss', '@include font("' + fontname + '","'  + fontname + '", "400", "normal");\r\n', cb);
                }
                     c_fontname = fontname;
                    }
                }
            })
        }
    }

function cb () {}

let build = gulp.series(gulp.parallel(css, html, images, fonts), fontsStyle);
let watch = gulp.parallel(build, watchFiles, browserSync);

exports.fontsStyle = fontsStyle;
exports.fonts = fonts;
exports.images = images;
exports.js = js;
exports.css = css;
exports.html = html;
exports.build = build;
exports.watch = watch;
exports.default = watch;

package.json

{
  "name": "gulp",
  "version": "1.0.0",
  "description": "My first gulp project",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Shamil",
  "license": "ISC",
  "devDependencies": {
    "browser-sync": "^2.26.13",
    "gulp": "^4.0.2",
    "gulp-autoprefixer": "^7.0.1",
    "gulp-clean-css": "^4.3.0",
    "gulp-file-include": "^2.2.2",
    "gulp-fonter": "^0.3.0",
    "gulp-group-css-media-queries": "^1.2.2",
    "gulp-imagemin": "^7.1.0",
    "gulp-minify-css": "^1.2.4",
    "gulp-rename": "^2.0.0",
    "gulp-sass": "^4.1.0",
    "gulp-svg-sprite": "^1.5.0",
    "gulp-ttf2woff": "^1.1.1",
    "gulp-ttf2woff2": "^3.0.0",
    "gulp-uglify-es": "^2.0.0",
    "gulp-webp": "^4.0.1",
    "gulp-webp-html": "^1.0.2",
    "gulp-webpcss": "^1.1.1",
    "node-sass": "^5.0.0",
    "webp-converter": "^2.2.3"
  }
}

HELPME

Answer 1

Well, elementary

let watch = gulp.parallel(build, watchFiles, browserSync);

You are trying to run the watchFiles task, but where is it?
What do you write in white on black.