Run command.

def run(self):
        """Run command."""
        if self.already_run:
            return
        package = self.distribution.packages[0]
        if os.path.exists("gulpfile.js") or os.path.exists("webpack.config.js"):
            yarn_version = check_output("yarn --version")
            npm_version = check_output("npm -v")
            print("yarn:", yarn_version, "npm: ", npm_version)
            if yarn_version != "":
                npm_bin = check_output("yarn bin").strip()
            else:
                assert npm_version != "", "need nodejs and one of npm or yarn installed in current PATH"
                assert LooseVersion(npm_version) >= LooseVersion(
                    "1.4"), "npm < 1.4 (%s)" % (npm_version)
                npm_bin = check_output("npm bin").strip()

            commands = []

            # if we find yarn, then we use it as it is much faster
            if yarn_version != "":
                commands.append(['yarn', 'install', '--pure-lockfile'])
            else:
                commands.append(['npm', 'install'])

            if os.path.exists("gulpfile.js"):
                commands.append([os.path.join(npm_bin, "gulp"), 'prod', '--notests'])
            elif os.path.exists("webpack.config.js"):
                commands.append([os.path.join(npm_bin, "webpack"), '-p'])

            shell = bool(os.name == 'nt')

            for command in commands:
                self.announce(
                    'Running command: %s' % str(" ".join(command)),
                    level=distutils.log.INFO)
                subprocess.check_call(command, shell=shell)

        self.copy_tree(os.path.join(package, 'static'), os.path.join(
            "build", "lib", package, "static"))

        with open(os.path.join("build", "lib", package, "VERSION"), "w") as f:
            f.write(self.distribution.metadata.version)

        with open(os.path.join(package, "VERSION"), "w") as f:
            f.write(self.distribution.metadata.version)

        self.already_run = True