Provide placeholder functions for lifecycle methods (can't provide pl…

…aceholder for `shouldUpdate` as some renderers need to check if it exists)

packages/metal-component/src/Component.js

@@ -28,9 +28,6 @@ import { EventEmitter, EventHandler } from 'metal-events';
  *   created() {
  *   }
  *
- *   willUpdate() {
- *   }
- *
  *   rendered() {
  *   }
  *
@@ -40,6 +37,19 @@ import { EventEmitter, EventHandler } from 'metal-events';
  *   attached() {
  *   }
  *
+ *   willReceiveState() {
+ *   }
+ *
+ *   // willReceiveProps is only available in JSX components
+ *   willReceiveProps() {
+ *   }
+ *
+ *   shouldUpdate() {
+ *   }
+ *
+ *   willUpdate() {
+ *   }
+ *
  *   willDetach() {
  *   }
  *
@@ -417,9 +427,7 @@ class Component extends EventEmitter {
 	 * @protected
 	 */
 	handleStateWillChange_(event) {
-		if (this.willReceiveState) {
-			this.willReceiveState(event.changes);
-		}
+		this.willReceiveState(event.changes);
 	}
 
 	/**
@@ -448,6 +456,15 @@ class Component extends EventEmitter {
 		this.emit('rendered', firstRender);
 	}
 
+	/**
+	 * Informs the component that the renderer is about to update. Calls the
+	 * component's `willUpdate` lifecycle method.
+	 * @param {Object} changes
+	 */
+	informWillUpdate(...args) {
+		this.willUpdate(...args);
+	}
+
 	/**
 	 * Checks if the given function is a component constructor.
 	 * @param {!function()} fn Any function
@@ -715,6 +732,20 @@ class Component extends EventEmitter {
 	 * Lifecycle. Fires before component is detached from the DOM.
 	 */
 	willDetach() {}
+
+	/**
+	 * Lifecycle. Called when the component is about to receive state changes.
+	 * Provides a hook point for modifying state that can be used in the next
+	 * rerender.
+	 * @param {Object} changes Changes made to this.state
+	 */
+	willReceiveState() {}
+
+	/**
+	 * Lifecycle. Called when the component's renderer is about to update.
+	 * @param {Object} changes
+	 */
+	willUpdate() {}
 }
 
 /**

packages/metal-incremental-dom/src/IncrementalDomRenderer.js

@@ -236,10 +236,10 @@ class IncrementalDomRenderer extends ComponentRenderer.constructor {
 	 * @param {Object} changes
 	 */
 	willUpdate_(component, changes) {
-		if (!component.willUpdate || !component.wasRendered || !changes) {
+		if (!component.wasRendered || !changes) {
 			return;
 		}
-		component.willUpdate(...this.buildShouldUpdateArgs(changes));
+		component.informWillUpdate(...this.buildShouldUpdateArgs(changes));
 	}
 }
 

packages/metal-jsx/src/JSXComponent.js

@@ -40,7 +40,7 @@ class JSXComponent extends Component {
 	 * @protected
 	 */
 	handleStateWillChange_(event) {
-		if (event.type !== 'state' && this.willReceiveProps) {
+		if (event.type !== 'state') {
 			this.willReceiveProps(event.changes);
 		}
 	}
@@ -64,6 +64,14 @@ class JSXComponent extends Component {
 
 		return retObj;
 	}
+
+	/**
+	 * Lifecycle. Called when the component is about to receive new props.
+	 * Provides a hook point for modifying state that can be used in the next
+	 * rerender.
+	 * @param {Object} changes Changes made to this.props
+	 */
+	willReceiveProps() {}
 }
 
 JSXComponent.DATA_MANAGER = JSXDataManager;