working sourcemap grunt sass

Gruntfile.js

module.exports = function(grunt) { // The general grunt function that is run

    //local folders
    const srcSassFolder = 'sass';
    const srcJsFolder = 'js';

    const publicCssFolder = 'public/css';
    const publicJsFolder = 'public/js';

    grunt.initConfig({ // Here we setup our config object with package.json and all the tasks

        pkg: grunt.file.readJSON('package.json'),

        sass: { // Begin sass tasks
            dist: {
                options: {
                    sourceMap: true,
                    style: 'expanded'
                },
                files: [{
                    expand: true,
                    cwd: 'sass',
                    src: ['*.scss'],
                    dest: publicCssFolder,
                    ext: '.css'
                }]
            }
        },

        postcss: { // Begin Post CSS Plugin
            options: {
                map: true,
                processors: [
                    require('autoprefixer')({
                        browsers: ['last 3 versions']
                    })
                ]
            },
            dist: {
                src: publicCssFolder + '/*.css'
            }
        },

        cssmin: { // Begin CSS Minify Plugin
           options: {
             sourceMap: true
           },
            target: {
                files: [{
                    expand: true,
                    cwd: publicCssFolder,
                    src: ['*.css', '!*.min.css'],
                    dest: publicCssFolder,
                    ext: '.min.css'
                }]
            }
        },

        uglify: { // Begin JS Uglify Plugin
            build: {
                files: [{
                    expand: true,
                    cwd: srcJsFolder,
                    src: '*.js',
                    dest: publicJsFolder,
                    ext: '.min.js'
                }]
            }
        },

        watch: { // Watch task for general work
            options: { banner: 'dsad'},
            css: {
                files: srcSassFolder + '/**/*.scss',
                tasks: ['sass', 'postcss', 'cssmin']
            },
            js: {
                files: srcJsFolder + '/**/*.js',
                tasks: ['uglify']
            }
        }
    });

    // All the plugins that is needed for above tasks
    grunt.loadNpmTasks('grunt-sass');
    grunt.loadNpmTasks('grunt-contrib-cssmin');
    grunt.loadNpmTasks('grunt-contrib-watch');
    grunt.loadNpmTasks('grunt-postcss');
    grunt.loadNpmTasks('grunt-contrib-uglify');

    // Registering the default task that we're going to use along with watch
    grunt.registerTask('styles', ['sass', 'postcss', 'cssmin']);
    grunt.registerTask('javascript', ['uglify']);
    grunt.registerTask('default', ['watch']);
};