[feature] replace undefined prop values with defaultProps (#60)

- mimick preact behaviour
- fix #58

Author: ftes

src/util.js

@@ -39,15 +39,37 @@ export function styleObjToCss(s) {
 	return str || undefined;
 }
 
+/**
+ * Copy all properties from `props` onto `obj`.
+ * @param {object} obj Object onto which properties should be copied.
+ * @param {object} props Object from which to copy properties.
+ * @returns {object}
+ * @private
+ */
 export function assign(obj, props) {
 	for (let i in props) obj[i] = props[i];
 	return obj;
 }
 
+/**
+ * Reconstruct Component-style `props` from a VNode.
+ * Ensures default/fallback values from `defaultProps`:
+ * Own-properties of `defaultProps` not present in `vnode.attributes` are added.
+ * @param {import('preact').VNode} vnode The VNode to get props for
+ * @returns {object} The props to use for this VNode
+ */
 export function getNodeProps(vnode) {
-	let defaultProps = vnode.nodeName.defaultProps,
-		props = assign({}, defaultProps || vnode.attributes);
-	if (defaultProps) assign(props, vnode.attributes);
-	if (vnode.children) props.children = vnode.children;
+	let props = assign({}, vnode.attributes);
+	props.children = vnode.children;
+
+	let defaultProps = vnode.nodeName.defaultProps;
+	if (defaultProps!==undefined) {
+		for (let i in defaultProps) {
+			if (props[i]===undefined) {
+				props[i] = defaultProps[i];
+			}
+		}
+	}
+
 	return props;
 }

test/render.js

@@ -221,8 +221,9 @@ describe('render', () => {
 			};
 
 			expect(render(<Test />), 'defaults').to.equal('<div foo="default foo" bar="default bar"></div>');
-			expect(render(<Test bar="b" />), 'partial').to.equal('<div foo="default foo" bar="b"></div>');
+			expect(render(<Test bar="b" />), 'partial').to.equal('<div bar="b" foo="default foo"></div>');
 			expect(render(<Test foo="a" bar="b" />), 'overridden').to.equal('<div foo="a" bar="b"></div>');
+			expect(render(<Test foo={undefined} bar="b" />), 'overridden').to.equal('<div foo="default foo" bar="b"></div>');
 		});
 	});
 
@@ -304,8 +305,9 @@ describe('render', () => {
 			};
 
 			expect(render(<Test />), 'defaults').to.equal('<div foo="default foo" bar="default bar"></div>');
-			expect(render(<Test bar="b" />), 'partial').to.equal('<div foo="default foo" bar="b"></div>');
+			expect(render(<Test bar="b" />), 'partial').to.equal('<div bar="b" foo="default foo"></div>');
 			expect(render(<Test foo="a" bar="b" />), 'overridden').to.equal('<div foo="a" bar="b"></div>');
+			expect(render(<Test foo={undefined} bar="b" />), 'overridden').to.equal('<div foo="default foo" bar="b"></div>');
 		});
 
 		it('should invoke componentWillMount', () => {