add beforeProperties lifecycle hook

src/WidgetBase.ts

@@ -7,6 +7,7 @@ import { isWNode, v, isHNode } from './d';
 import { auto, ignore } from './diff';
 import {
 	AfterRender,
+	BeforeProperties,
 	BeforeRender,
 	CoreProperties,
 	DiffPropertyFunction,
@@ -361,7 +362,8 @@ export class WidgetBase<P = WidgetProperties, C extends DNode = DNode> extends E
 		this._coreProperties = coreProperties;
 	}
 
-	public __setProperties__(properties: this['properties']): void {
+	public __setProperties__(originalProperties: this['properties']): void {
+		const properties = this._runBeforeProperties(originalProperties);
 		const changedPropertyKeys: string[] = [];
 		const allProperties = [ ...Object.keys(properties), ...Object.keys(this._properties) ];
 		const checkedProperties: string[] = [];
@@ -378,7 +380,7 @@ export class WidgetBase<P = WidgetProperties, C extends DNode = DNode> extends E
 			}
 			checkedProperties.push(propertyName);
 			const previousProperty = this._properties[propertyName];
-			const newProperty = this._bindFunctionProperty((properties as any)[propertyName], this._coreProperties.bind);
+			const newProperty = this._bindFunctionProperty(properties[propertyName], this._coreProperties.bind);
 			if (registeredDiffPropertyNames.indexOf(propertyName) !== -1) {
 				runReactions = true;
 				const diffFunctions = this.getDecorator(`diffProperty:${propertyName}`);
@@ -633,6 +635,16 @@ export class WidgetBase<P = WidgetProperties, C extends DNode = DNode> extends E
 		return this._registries;
 	}
 
+	private _runBeforeProperties(properties: any) {
+		const beforeProperties: BeforeProperties[] = this.getDecorator('beforeProperties');
+		if (beforeProperties.length > 0) {
+			return beforeProperties.reduce((properties, beforePropertiesFunction) => {
+				return { ...properties, ...beforePropertiesFunction(properties) };
+			}, { ...properties });
+		}
+		return properties;
+	}
+
 	/**
 	 * Run all registered before renders and return the updated render method
 	 */

src/decorators/beforeProperties.ts

@@ -0,0 +1,15 @@
+import { handleDecorator } from './../WidgetBase';
+import { BeforeProperties } from './../interfaces';
+
+/**
+ *
+ */
+export function beforeProperties(method: BeforeProperties): (target: any) => void;
+export function beforeProperties(): (target: any, propertyKey: string) => void;
+export function beforeProperties(method?: BeforeProperties) {
+	return handleDecorator((target, propertyKey) => {
+		target.addDecorator('beforeProperties', propertyKey ? target[propertyKey] : method);
+	});
+}
+
+export default beforeProperties;

src/interfaces.d.ts

@@ -442,3 +442,10 @@ export interface BeforeRender {
 export interface AfterRender {
 	(dNode: DNode | DNode []): DNode | DNode[];
 }
+
+/**
+ * Interface for beforeProperties function
+ */
+export interface BeforeProperties<P = any> {
+	(properties: P): P;
+}

tests/unit/all.ts

@@ -5,6 +5,7 @@ import './WidgetRegistry';
 import './lifecycle';
 import './customElements';
 import './d';
+import './decorators/all';
 import './mixins/all';
 import './util/all';
 import './main';

tests/unit/decorators/all.ts

@@ -0,0 +1 @@
+import './beforeProperties';

tests/unit/decorators/beforeProperties.ts

@@ -0,0 +1,69 @@
+import * as registerSuite from 'intern!object';
+import * as assert from 'intern/chai!assert';
+
+import { beforeProperties } from './../../../src/decorators/beforeProperties';
+import { WidgetBase } from './../../../src/WidgetBase';
+import { WidgetProperties } from './../../../src/interfaces';
+
+registerSuite({
+	name: 'decorators/beforeProperties',
+	beforeProperties() {
+		function before(properties: WidgetProperties): WidgetProperties {
+			return { key: 'foo' };
+		}
+
+		@beforeProperties(before)
+		class TestWidget extends WidgetBase<any> {}
+		const widget = new TestWidget();
+		widget.__setProperties__({});
+		assert.strictEqual(widget.properties.key, 'foo');
+	},
+	'multiple beforeProperties decorators'() {
+		function beforeOne(properties: WidgetProperties): WidgetProperties {
+			return { key: 'foo' };
+		}
+		function beforeTwo(properties: any): any {
+			return { other: 'bar' };
+		}
+
+		@beforeProperties(beforeOne)
+		@beforeProperties(beforeTwo)
+		class TestWidget extends WidgetBase<any> {}
+		const widget = new TestWidget();
+		widget.__setProperties__({});
+		assert.strictEqual(widget.properties.key, 'foo');
+		assert.strictEqual(widget.properties.other, 'bar');
+	},
+	'beforeProperties on class method'() {
+		class TestWidget extends WidgetBase<any> {
+			@beforeProperties()
+			before(properties: WidgetProperties): WidgetProperties {
+				return { key: 'foo' };
+			}
+		}
+		const widget = new TestWidget();
+		widget.__setProperties__({});
+		assert.strictEqual(widget.properties.key, 'foo');
+
+	},
+	'programmatic beforeProperties'() {
+		function beforeOne(properties: WidgetProperties): WidgetProperties {
+			return { key: 'foo' };
+		}
+		function beforeTwo(properties: any): any {
+			return { other: 'bar' };
+		}
+
+		class TestWidget extends WidgetBase<any> {
+			constructor() {
+				super();
+				beforeProperties(beforeOne)(this);
+				beforeProperties(beforeTwo)(this);
+			}
+		}
+		const widget = new TestWidget();
+		widget.__setProperties__({});
+		assert.strictEqual(widget.properties.key, 'foo');
+		assert.strictEqual(widget.properties.other, 'bar');
+	}
+});