npm install cpx

Usage: cpx <source> <dest> [options]

    Copy files, watching for changes.

        <source>  The glob of target files.
        <dest>    The path of a destination directory.

Options:

    -c, --command <command>   A command text to transform each file.
    -C, --clean               Clean files that matches <source> like pattern in
                              <dest> directory before the first copying.
    -L, --dereference         Follow symbolic links when copying from them.
    -h, --help                Print usage information.
    --include-empty-dirs      The flag to copy empty directories which is
                              matched with the glob.
    --no-initial              The flag to not copy at the initial time of watch.
                              Use together '--watch' option.
    -p, --preserve            The flag to copy attributes of files.
                              This attributes are uid, gid, atime, and mtime.
    -t, --transform <name>    A module name to transform each file. cpx lookups
                                the specified name via "require()".
    -u, --update              The flag to not overwrite files on destination if
                              the source file is older.
    -v, --verbose             Print copied/removed files.
    -V, --version             Print the version number.
    -w, --watch               Watch for files that matches <source>, and copy
                              the file to <dest> every changing.

cpx "src/**/*.{html,png,jpg}" app --watch