gulp + browser-sync Cannot GET / error

Question

I am learning the front-end build system currently gulp, i want to use brower-sync and the problem is it is not throwing an error in the commad line but instead when it brings

Answer 1

gulp.task('serve',['sass'], function() {
    bs.init({
        server: "./app",
        startPath: "/index.html", // After it browser running
        browser: 'chrome',
        host: 'localhost',
        port: 4000,
        open: true,
        tunnel: true
    });

Answer 2

gulp.task('browser-sync', function() {
    browserSync({

      server: {
            baseDir: "./"
            },

            port: 8080,
            open: true,
            notify: false
    });
});