Pagekit\Installer\Helper\Composer::composerUpdate PHP Method

    protected function composerUpdate($updates = false, $refresh = [], $packagist = false, $preferSource = false)
    {
        $installed = new JsonFile($this->paths['path.vendor'] . '/composer/installed.json');
        $internal = new CompositeRepository([]);
        $internal->addRepository(new InstalledFilesystemRepository($installed));
        $composer = $this->getComposer($packagist);
        $composer->getDownloadManager()->setOutputProgress(false);
        $local = $composer->getRepositoryManager()->getLocalRepository();
        foreach ($refresh as $package) {
            $local->removePackage($package);
        }
        $installer = Installer::create($this->getIO(), $composer)->setAdditionalInstalledRepository($internal)->setOptimizeAutoloader(true)->setUpdate(true);
        if ($preferSource) {
            $installer->setPreferSource(true);
        } else {
            $installer->setPreferDist(true);
        }
        if ($updates) {
            $installer->setUpdateWhitelist($updates)->setWhitelistDependencies();
        }
        $installer->run();
    }