diff --git a/Makefile b/Makefile
index 34c6a1d..6de61c0 100644
--- a/Makefile
+++ b/Makefile
@@ -18,5 +18,5 @@ install:
 .PHONY: test coverage open-coverage lint install
 
 test/bin/php-cs-fixer:
-	curl -sSL http://cs.sensiolabs.org/download/php-cs-fixer-v2.phar -o test/bin/php-cs-fixer
+	curl -sSL https://cs.sensiolabs.org/download/php-cs-fixer-v2.phar -o test/bin/php-cs-fixer
 	chmod +x test/bin/php-cs-fixer
diff --git a/README.md b/README.md
index 23600ae..43fab7b 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,31 @@ a dependency.
 [npm]: https://npmjs.org/
 [update]: https://npmjs.org/doc/update.html
 
+## Configuration
+
+The following configuration can be added to `composer.json` `extra/npm-bridge`
+to customize the behaviour on a per-package basis. Values in the root package
+will not currently impact any dependency packages that also use
+`composer-npm-bridge` - each package must define its own options.
+
+Key|Description
+-|-
+`timeout`|Specify a custom timeout for the installation. The default is 300 seconds.
+`optional`|Skip instead of throwing an exception if `npm` is not found when processing the package.
+
+    ...
+    "extra": {
+        "npm-bridge": {
+            "timeout": 9000,
+            "optional": true
+        },
+        ...
+    }
+
+To disable `composer-npm-bridge` entirely for a single run, set `COMPOSER_NPM_BRIDGE_DISABLE=1` on the environment.
+
+    COMPOSER_NPM_BRIDGE_DISABLE=1 composer install
+
 ## Caveats
 
 Because NPM dependencies are installed underneath the root directory of the
diff --git a/src/NpmBridge.php b/src/NpmBridge.php
index a626d3f..afe5467 100644
--- a/src/NpmBridge.php
+++ b/src/NpmBridge.php
@@ -13,6 +13,10 @@
  */
 class NpmBridge
 {
+    const EXTRA_KEY = 'npm-bridge';
+    const EXTRA_KEY_OPTIONAL = 'optional';
+    const EXTRA_KEY_TIMEOUT = 'timeout';
+
     /**
      * Construct a new Composer NPM bridge plugin.
      *
@@ -47,8 +51,12 @@ public function install(Composer $composer, bool $isDevMode = true)
             '<info>Installing NPM dependencies for root project</info>'
         );
 
-        if ($this->isDependantPackage($composer->getPackage(), $isDevMode)) {
-            $this->client->install(null, $isDevMode);
+        $package = $composer->getPackage();
+        if ($this->isDependantPackage($package, $isDevMode)) {
+            if (!$this->shouldSkipPackage($package)) {
+                $this->configureClient($package);
+                $this->client->install(null, $isDevMode);
+            }
         } else {
             $this->io->write('Nothing to install');
         }
@@ -70,9 +78,13 @@ public function update(Composer $composer)
             '<info>Updating NPM dependencies for root project</info>'
         );
 
-        if ($this->isDependantPackage($composer->getPackage(), true)) {
-            $this->client->update();
-            $this->client->install(null, true);
+        $package = $composer->getPackage();
+        if ($this->isDependantPackage($package, true)) {
+            if (!$this->shouldSkipPackage($package)) {
+                $this->configureClient($package);
+                $this->client->update();
+                $this->client->install(null, true);
+            }
         } else {
             $this->io->write('Nothing to update');
         }
@@ -119,6 +131,10 @@ private function installForVendors($composer)
 
         if (count($packages) > 0) {
             foreach ($packages as $package) {
+                if ($this->shouldSkipPackage($package)) {
+                    continue;
+                }
+
                 $this->io->write(
                     sprintf(
                         '<info>Installing NPM dependencies for %s</info>',
@@ -126,6 +142,7 @@ private function installForVendors($composer)
                     )
                 );
 
+                $this->configureClient($package);
                 $this->client->install(
                     $composer->getInstallationManager()
                         ->getInstallPath($package),
@@ -137,6 +154,38 @@ private function installForVendors($composer)
         }
     }
 
+    private function configureClient(PackageInterface $package)
+    {
+        $extra = $package->getExtra();
+        // Issue #13 - npm can take a while, so allow a custom timeout
+        if (isset($extra[self::EXTRA_KEY][self::EXTRA_KEY_TIMEOUT])) {
+            $this->client->setTimeout(intval($extra[self::EXTRA_KEY][self::EXTRA_KEY_TIMEOUT]));
+        } else {
+            $this->client->setTimeout(null);
+        }
+    }
+
+    private function shouldSkipPackage(PackageInterface $package)
+    {
+        if ($this->client->valid()) {
+            return false;
+        }
+
+        $extra = $package->getExtra();
+        if (!empty($extra[self::EXTRA_KEY][self::EXTRA_KEY_OPTIONAL])) {
+            $this->io->write(
+                sprintf(
+                    '<info>Skipping optional NPM dependencies for %s as npm is unavailable</info>',
+                    $package->getPrettyName()
+                )
+            );
+
+            return true;
+        }
+
+        return false;
+    }
+
     private $io;
     private $vendorFinder;
     private $client;
diff --git a/src/NpmBridgePlugin.php b/src/NpmBridgePlugin.php
index a9a9d75..c292273 100644
--- a/src/NpmBridgePlugin.php
+++ b/src/NpmBridgePlugin.php
@@ -52,9 +52,15 @@ class_exists(NpmVendorFinder::class);
      */
     public static function getSubscribedEvents(): array
     {
+        // Issue #18 - disable if ENV set
+        if (!empty(getenv('COMPOSER_NPM_BRIDGE_DISABLE'))) {
+            return [];
+        }
+
+        // Increased priority to ensure we run before custom installers which are usually default priority
         return [
-            ScriptEvents::POST_INSTALL_CMD => 'onPostInstallCmd',
-            ScriptEvents::POST_UPDATE_CMD => 'onPostUpdateCmd',
+            ScriptEvents::POST_INSTALL_CMD => ['onPostInstallCmd', 1],
+            ScriptEvents::POST_UPDATE_CMD => ['onPostUpdateCmd', 1],
         ];
     }
 
diff --git a/src/NpmClient.php b/src/NpmClient.php
index 199cdd3..e1ffcf9 100644
--- a/src/NpmClient.php
+++ b/src/NpmClient.php
@@ -43,6 +43,7 @@ public function __construct(
         $this->executableFinder = $executableFinder;
         $this->getcwd = $getcwd;
         $this->chdir = $chdir;
+        $this->timeout = null;
     }
 
     /**
@@ -78,6 +79,32 @@ public function update(string $path = null)
         $this->executeNpm(['update'], $path);
     }
 
+    /**
+     * Set timeout. Null to use default
+     *
+     * @param int|null $timeout
+     */
+    public function setTimeout($timeout)
+    {
+        $this->timeout = $timeout;
+    }
+
+    /**
+     * Check is npm is available
+     *
+     * @return bool
+     */
+    public function valid()
+    {
+        try {
+            $this->npmPath();
+        } catch (NpmNotFoundException $err) {
+            return false;
+        }
+
+        return true;
+    }
+
     private function executeNpm($arguments, $workingDirectoryPath)
     {
         array_unshift($arguments, $this->npmPath());
@@ -88,7 +115,14 @@ private function executeNpm($arguments, $workingDirectoryPath)
             call_user_func($this->chdir, $workingDirectoryPath);
         }
 
+        if (null !== $this->timeout) {
+            $oldTimeout = $this->processExecutor->getTimeout();
+            $this->processExecutor->setTimeout($this->timeout);
+        }
         $exitCode = $this->processExecutor->execute($command);
+        if (null !== $this->timeout) {
+            $this->processExecutor->setTimeout($oldTimeout);
+        }
 
         if (null !== $workingDirectoryPath) {
             call_user_func($this->chdir, $previousWorkingDirectoryPath);
diff --git a/test/suite/NpmBridgePluginTest.php b/test/suite/NpmBridgePluginTest.php
index d411d82..9d129a9 100644
--- a/test/suite/NpmBridgePluginTest.php
+++ b/test/suite/NpmBridgePluginTest.php
@@ -47,10 +47,17 @@ public function testActivate()
 
     public function testGetSubscribedEvents()
     {
+        putenv('COMPOSER_NPM_BRIDGE_DISABLE=1');
+        $this->assertSame(
+            [],
+            $this->plugin->getSubscribedEvents()
+        );
+        putenv('COMPOSER_NPM_BRIDGE_DISABLE=');
+
         $this->assertSame(
             [
-                ScriptEvents::POST_INSTALL_CMD => 'onPostInstallCmd',
-                ScriptEvents::POST_UPDATE_CMD => 'onPostUpdateCmd',
+                ScriptEvents::POST_INSTALL_CMD => ['onPostInstallCmd', 1],
+                ScriptEvents::POST_UPDATE_CMD => ['onPostUpdateCmd', 1],
             ],
             $this->plugin->getSubscribedEvents()
         );
diff --git a/test/suite/NpmBridgeTest.php b/test/suite/NpmBridgeTest.php
index 7d5d84a..51d2265 100644
--- a/test/suite/NpmBridgeTest.php
+++ b/test/suite/NpmBridgeTest.php
@@ -6,6 +6,7 @@
 use Composer\Package\Link;
 use Composer\Package\Package;
 use Composer\Package\RootPackage;
+use Eloquent\Composer\NpmBridge\Exception\NpmNotFoundException;
 use Eloquent\Phony\Phpunit\Phony;
 use PHPUnit\Framework\TestCase;
 
@@ -16,6 +17,7 @@ protected function setUp()
         $this->io = Phony::mock('Composer\IO\IOInterface');
         $this->vendorFinder = Phony::mock('Eloquent\Composer\NpmBridge\NpmVendorFinder');
         $this->client = Phony::mock('Eloquent\Composer\NpmBridge\NpmClient');
+        $this->client->valid->returns(true);
         $this->bridge = new NpmBridge($this->io->get(), $this->vendorFinder->get(), $this->client->get());
 
         $this->composer = new Composer();
@@ -23,6 +25,9 @@ protected function setUp()
         $this->rootPackage = new RootPackage('vendor/package', '1.0.0.0', '1.0.0');
         $this->packageA = new Package('vendorA/packageA', '1.0.0.0', '1.0.0');
         $this->packageB = new Package('vendorB/packageB', '1.0.0.0', '1.0.0');
+        $this->packageC = new Package('vendorC/packageC', '1.0.0.0', '1.0.0');
+
+        $this->packageC->setExtra([NpmBridge::EXTRA_KEY => [NpmBridge::EXTRA_KEY_OPTIONAL => true, NpmBridge::EXTRA_KEY_TIMEOUT => 900]]);
 
         $this->linkRoot1 = new Link('vendor/package', 'vendorX/packageX');
         $this->linkRoot2 = new Link('vendor/package', 'vendorY/packageY');
@@ -31,6 +36,7 @@ protected function setUp()
         $this->installationManager = Phony::mock('Composer\Installer\InstallationManager');
         $this->installationManager->getInstallPath->with($this->packageA)->returns('/path/to/install/a');
         $this->installationManager->getInstallPath->with($this->packageB)->returns('/path/to/install/b');
+        $this->installationManager->getInstallPath->with($this->packageC)->returns('/path/to/install/c');
 
         $this->composer->setPackage($this->rootPackage);
         $this->composer->setInstallationManager($this->installationManager->get());
@@ -39,34 +45,48 @@ protected function setUp()
     public function testInstall()
     {
         $this->rootPackage->setRequires([$this->linkRoot1, $this->linkRoot2, $this->linkRoot3]);
-        $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([$this->packageA, $this->packageB]);
+        $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([$this->packageA, $this->packageB, $this->packageC]);
         $this->bridge->install($this->composer);
 
         Phony::inOrder(
             $this->io->write->calledWith('<info>Installing NPM dependencies for root project</info>'),
+            $this->client->valid->calledWith(),
             $this->client->install->calledWith(null, true),
             $this->io->write->calledWith('<info>Installing NPM dependencies for Composer dependencies</info>'),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorA/packageA</info>'),
             $this->client->install->calledWith('/path/to/install/a', false),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorB/packageB</info>'),
-            $this->client->install->calledWith('/path/to/install/b', false)
+            $this->client->install->calledWith('/path/to/install/b', false),
+            $this->client->valid->calledWith(),
+            $this->io->write->calledWith('<info>Installing NPM dependencies for vendorC/packageC</info>'),
+            $this->client->setTimeout->calledWith(900),
+            $this->client->install->calledWith('/path/to/install/c', false)
         );
     }
 
     public function testInstallProductionMode()
     {
         $this->rootPackage->setRequires([$this->linkRoot1, $this->linkRoot2, $this->linkRoot3]);
-        $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([$this->packageA, $this->packageB]);
+        $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([$this->packageA, $this->packageB, $this->packageC]);
         $this->bridge->install($this->composer, false);
 
         Phony::inOrder(
             $this->io->write->calledWith('<info>Installing NPM dependencies for root project</info>'),
+            $this->client->valid->calledWith(),
             $this->client->install->calledWith(null, false),
             $this->io->write->calledWith('<info>Installing NPM dependencies for Composer dependencies</info>'),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorA/packageA</info>'),
             $this->client->install->calledWith('/path/to/install/a', false),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorB/packageB</info>'),
-            $this->client->install->calledWith('/path/to/install/b', false)
+            $this->client->install->calledWith('/path/to/install/b', false),
+            $this->client->valid->calledWith(),
+            $this->io->write->calledWith('<info>Installing NPM dependencies for vendorC/packageC</info>'),
+            $this->client->setTimeout->calledWith(900),
+            $this->client->install->calledWith('/path/to/install/c', false)
         );
     }
 
@@ -76,6 +96,7 @@ public function testInstallRootDevDependenciesInDevMode()
         $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([]);
         $this->bridge->install($this->composer, true);
 
+        $this->client->valid->calledWith();
         $this->client->install->calledWith(null, true);
     }
 
@@ -102,6 +123,31 @@ public function testInstallNothing()
         );
     }
 
+    public function testInstallOptional()
+    {
+        $this->client->valid->returns(false);
+        $this->client->install->with('/path/to/install/a')->throws(NpmNotFoundException::class);
+        $this->client->install->with('/path/to/install/c')->returns();
+
+        $this->rootPackage->setRequires([$this->linkRoot1, $this->linkRoot2]);
+        $this->vendorFinder->find->with($this->composer, $this->bridge)->returns([$this->packageC, $this->packageA]);
+        try {
+            $this->bridge->install($this->composer);
+        } catch (Exception $err) {
+        }
+
+        Phony::inOrder(
+            $this->io->write->calledWith('<info>Installing NPM dependencies for root project</info>'),
+            $this->io->write->calledWith('Nothing to install'),
+            $this->io->write->calledWith('<info>Installing NPM dependencies for Composer dependencies</info>'),
+            $this->client->valid->calledWith(),
+            $this->io->write->calledWith('<info>Skipping optional NPM dependencies for vendorC/packageC as npm is unavailable</info>'),
+            $this->client->valid->calledWith(),
+            $this->io->write->calledWith('<info>Installing NPM dependencies for vendorA/packageA</info>'),
+            $this->client->install->calledWith('/path/to/install/a', false)
+        );
+    }
+
     public function testUpdate()
     {
         $this->rootPackage->setRequires([$this->linkRoot1, $this->linkRoot2, $this->linkRoot3]);
@@ -110,11 +156,14 @@ public function testUpdate()
 
         Phony::inOrder(
             $this->io->write->calledWith('<info>Updating NPM dependencies for root project</info>'),
+            $this->client->valid->calledWith(),
             $this->client->update->calledWith(),
             $this->client->install->calledWith(null, true),
             $this->io->write->calledWith('<info>Installing NPM dependencies for Composer dependencies</info>'),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorA/packageA</info>'),
             $this->client->install->calledWith('/path/to/install/a', false),
+            $this->client->valid->calledWith(),
             $this->io->write->calledWith('<info>Installing NPM dependencies for vendorB/packageB</info>'),
             $this->client->install->calledWith('/path/to/install/b', false)
         );
diff --git a/test/suite/NpmClientTest.php b/test/suite/NpmClientTest.php
index 501883e..2e3637e 100644
--- a/test/suite/NpmClientTest.php
+++ b/test/suite/NpmClientTest.php
@@ -17,23 +17,47 @@ protected function setUp()
             new NpmClient($this->processExecutor->get(), $this->executableFinder->get(), $this->getcwd, $this->chdir);
 
         $this->processExecutor->execute->returns(0);
+        Phony::onStatic($this->processExecutor)->getTimeout->returns(300);
+        Phony::onStatic($this->processExecutor)->setTimeout->returns();
         $this->executableFinder->find->with('npm')->returns('/path/to/npm');
         $this->getcwd->returns('/path/to/cwd');
     }
 
     public function testInstall()
     {
-        $this->assertNull($this->client->install('/path/to/project'));
+        $this->assertNull($this->client->install());
+        Phony::inOrder(
+            $this->executableFinder->find->calledWith('npm'),
+            $this->processExecutor->execute->calledWith("'/path/to/npm' 'install'")
+        );
+        $this->chdir->never()->returned();
+        $this->processExecutor->setTimeout->never()->returned();
+    }
+
+    public function testInstallWorking()
+    {
         $this->assertNull($this->client->install('/path/to/project'));
         Phony::inOrder(
             $this->executableFinder->find->calledWith('npm'),
             $this->chdir->calledWith('/path/to/project'),
             $this->processExecutor->execute->calledWith("'/path/to/npm' 'install'"),
-            $this->chdir->calledWith('/path/to/cwd'),
-            $this->chdir->calledWith('/path/to/project'),
-            $this->processExecutor->execute->calledWith("'/path/to/npm' 'install'"),
             $this->chdir->calledWith('/path/to/cwd')
         );
+        $this->processExecutor->setTimeout->never()->returned();
+    }
+
+    public function testInstallTimeout()
+    {
+        $this->assertNull($this->client->setTimeout(900));
+        $this->assertNull($this->client->install());
+        Phony::inOrder(
+            $this->executableFinder->find->calledWith('npm'),
+            Phony::onStatic($this->processExecutor)->getTimeout->calledWith(),
+            Phony::onStatic($this->processExecutor)->setTimeout->calledWith(900),
+            $this->processExecutor->execute->calledWith("'/path/to/npm' 'install'"),
+            Phony::onStatic($this->processExecutor)->setTimeout->calledWith(300)
+        );
+        $this->chdir->never()->returned();
     }
 
     public function testInstallProductionMode()
@@ -65,17 +89,39 @@ public function testInstallFailureCommandFailed()
 
     public function testUpdate()
     {
-        $this->assertNull($this->client->update('/path/to/project'));
+        $this->assertNull($this->client->update());
+        Phony::inOrder(
+            $this->executableFinder->find->calledWith('npm'),
+            $this->processExecutor->execute->calledWith("'/path/to/npm' 'update'")
+        );
+        $this->chdir->never()->returned();
+        $this->processExecutor->setTimeout->never()->returned();
+    }
+
+    public function testUpdateWorking()
+    {
         $this->assertNull($this->client->update('/path/to/project'));
         Phony::inOrder(
             $this->executableFinder->find->calledWith('npm'),
             $this->chdir->calledWith('/path/to/project'),
             $this->processExecutor->execute->calledWith("'/path/to/npm' 'update'"),
-            $this->chdir->calledWith('/path/to/cwd'),
-            $this->chdir->calledWith('/path/to/project'),
-            $this->processExecutor->execute->calledWith("'/path/to/npm' 'update'"),
             $this->chdir->calledWith('/path/to/cwd')
         );
+        $this->processExecutor->setTimeout->never()->returned();
+    }
+
+    public function testUpdateTimeout()
+    {
+        $this->assertNull($this->client->setTimeout(900));
+        $this->assertNull($this->client->update());
+        Phony::inOrder(
+            $this->executableFinder->find->calledWith('npm'),
+            Phony::onStatic($this->processExecutor)->getTimeout->calledWith(),
+            Phony::onStatic($this->processExecutor)->setTimeout->calledWith(900),
+            $this->processExecutor->execute->calledWith("'/path/to/npm' 'update'"),
+            Phony::onStatic($this->processExecutor)->setTimeout->calledWith(300)
+        );
+        $this->chdir->never()->returned();
     }
 
     public function testUpdateFailureNpmNotFound()
@@ -93,4 +139,19 @@ public function testUpdateFailureCommandFailed()
         $this->expectException('Eloquent\Composer\NpmBridge\Exception\NpmCommandFailedException');
         $this->client->update('/path/to/project');
     }
+
+    public function testValid()
+    {
+        $this->executableFinder->find->with('npm')->returns(null);
+        $this->assertSame(
+            false,
+            $this->client->valid()
+        );
+
+        $this->executableFinder->find->with('npm')->returns('/path/to/npm');
+        $this->assertSame(
+            true,
+            $this->client->valid()
+        );
+    }
 }