diff --git a/framework/base/ViewContent.php b/framework/base/ViewContent.php
index e5a1a06..c7a3bc4 100644
--- a/framework/base/ViewContent.php
+++ b/framework/base/ViewContent.php
@@ -39,6 +39,7 @@ class ViewContent extends Component
 
 	public function reset()
 	{
+		$this->assetBundles = null;
 		$this->title = null;
 		$this->metaTags = null;
 		$this->linkTags = null;
diff --git a/framework/web/AssetBundle.php b/framework/web/AssetBundle.php
index 124f5e6..f82173b 100644
--- a/framework/web/AssetBundle.php
+++ b/framework/web/AssetBundle.php
@@ -122,11 +122,13 @@ class AssetBundle extends Object
 			list ($this->basePath, $this->baseUrl) = $am->publish($this->sourcePath, $this->publishOptions);
 		}
 
+		$converter = $am->getConverter();
+
 		foreach ($this->js as $js => $options) {
 			$js = is_string($options) ? $options : $js;
 			if (strpos($js, '/') !== 0 && strpos($js, '://') === false) {
 				if (isset($this->basePath, $this->baseUrl)) {
-					$js = $am->processAsset(ltrim($js, '/'), $this->basePath, $this->baseUrl);
+					$js = $converter->convert(ltrim($js, '/'), $this->basePath, $this->baseUrl);
 				} else {
 					throw new InvalidConfigException('Both of the "baseUrl" and "basePath" properties must be set.');
 				}
@@ -137,7 +139,7 @@ class AssetBundle extends Object
 			$css = is_string($options) ? $options : $css;
 			if (strpos($css, '//') !== 0 && strpos($css, '://') === false) {
 				if (isset($this->basePath, $this->baseUrl)) {
-					$css = $am->processAsset(ltrim($css, '/'), $this->basePath, $this->baseUrl);
+					$css = $converter->convert(ltrim($css, '/'), $this->basePath, $this->baseUrl);
 				} else {
 					throw new InvalidConfigException('Both of the "baseUrl" and "basePath" properties must be set.');
 				}
diff --git a/framework/web/AssetConverter.php b/framework/web/AssetConverter.php
new file mode 100644
index 0000000..26cc59b
--- /dev/null
+++ b/framework/web/AssetConverter.php
@@ -0,0 +1,45 @@
+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\web;
+
+use Yii;
+use yii\base\Component;
+
+/**
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+class AssetConverter extends Component implements IAssetConverter
+{
+	public $commands = array(
+		'less' => array('css', 'lessc %s %s'),
+		'scss' => array('css', 'sass %s %s'),
+		'sass' => array('css', 'sass %s %s'),
+		'styl' => array('js', 'stylus < %s > %s'),
+	);
+
+	public function convert($asset, $basePath, $baseUrl)
+	{
+		$pos = strrpos($asset, '.');
+		if ($pos !== false) {
+			$ext = substr($asset, $pos + 1);
+			if (isset($this->commands[$ext])) {
+				list ($ext, $command) = $this->commands[$ext];
+				$result = substr($asset, 0, $pos + 1) . $ext;
+				if (@filemtime("$basePath/$result") < filemtime("$basePath/$asset")) {
+					$output = array();
+					$command = sprintf($command, "$basePath/$asset", "$basePath/$result");
+					exec($command, $output);
+					Yii::info("Converted $asset into $result: " . implode("\n", $output), __METHOD__);
+					return "$baseUrl/$result";
+				}
+			}
+		}
+		return "$baseUrl/$asset";
+	}
+}
\ No newline at end of file
diff --git a/framework/web/AssetManager.php b/framework/web/AssetManager.php
index 72dd06b..c4ad385 100644
--- a/framework/web/AssetManager.php
+++ b/framework/web/AssetManager.php
@@ -26,13 +26,6 @@ class AssetManager extends Component
 	 */
 	public $bundles;
 	/**
-	 * @var array list of asset processors. An asset processor will convert a special type of asset files
-	 * (e.g. LESS, Sass, TypeScript) into JS or CSS files. The array keys are the file extension names
-	 * (e.g. "less", "sass", "ts"), and the array values are the corresponding configuration arrays
-	 * for creating the processor objects.
-	 */
-	public $processors;
-	/**
 	 * @return string the root directory storing the published asset files.
 	 */
 	public $basePath = '@wwwroot/assets';
@@ -139,26 +132,26 @@ class AssetManager extends Component
 		return $this->bundles[$name];
 	}
 
+	private $_converter;
+
 	/**
-	 * Processes the given asset file and returns a URL to the processed one.
-	 * This method can be overwritten to support various types of asset files, such as LESS, Sass, TypeScript.
-	 * @param string $asset the asset file path to be processed. The file path is relative
-	 * to $basePath, and it may contain forward slashes to indicate sub-directories (e.g. "js/main.js").
-	 * @param string $basePath the directory that contains the asset file.
-	 * @param string $baseUrl the corresponding URL of $basePath.
-	 * @return string the processed asset file path.
+	 * @return IAssetConverter
 	 */
-	public function processAsset($asset, $basePath, $baseUrl)
+	public function getConverter()
 	{
-		$ext = pathinfo($asset, PATHINFO_EXTENSION);
-		if (isset($this->processors[$ext])) {
-			if (is_array($this->processors[$ext])) {
-				$this->processors[$ext] = Yii::createObject($this->processors[$ext]);
-			}
-			return $this->processors[$ext]->process($asset, $basePath, $baseUrl);
-		} else {
-			return $baseUrl . '/' . $asset;
+		if ($this->_converter === null) {
+			$this->_converter = Yii::createObject(array(
+				'class' => 'yii\\web\\AssetConverter',
+			));
+		} elseif (is_array($this->_converter) || is_string($this->_converter)) {
+			$this->_converter = Yii::createObject($this->_converter);
 		}
+		return $this->_converter;
+	}
+
+	public function setConverter($value)
+	{
+		$this->_converter = $value;
 	}
 
 	/**
diff --git a/framework/web/IAssetConverter.php b/framework/web/IAssetConverter.php
new file mode 100644
index 0000000..994cb2f
--- /dev/null
+++ b/framework/web/IAssetConverter.php
@@ -0,0 +1,17 @@
+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\web;
+
+/**
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @since 2.0
+ */
+interface IAssetConverter
+{
+	public function convert($asset, $basePath, $baseUrl);
+}
\ No newline at end of file