fix: should call unmount (preactjs#1647)

Author: JoviDeCroock

src/render.js

@@ -21,7 +21,7 @@ export function render(vnode, parentDom, replaceNode) {
 	diffChildren(
 		parentDom,
 		replaceNode ? vnode : (parentDom._prevVNode = vnode),
-		replaceNode ? undefined : oldVNode,
+		oldVNode,
 		EMPTY_OBJ,
 		parentDom.ownerSVGElement !== undefined,
 		replaceNode

test/browser/render.test.js

@@ -996,6 +996,31 @@ describe('render()', () => {
 			expect(scratch.innerHTML).to.equal('<div id="a"></div><div id="b"></div><div id="c"></div>');
 		});
 
+		it('should unmount existing components', () => {
+			const newScratch = setupScratch();
+			const unmount = sinon.spy();
+			const mount = sinon.spy();
+			class App extends Component {
+				componentDidMount() {
+					mount();
+				}
+
+				componentWillUnmount() {
+					unmount();
+				}
+
+				render() {
+					return <div>App</div>;
+				}
+			}
+			render(<div id="a"><App /></div>, newScratch);
+			expect(newScratch.innerHTML).to.equal('<div id="a"><div>App</div></div>');
+			expect(mount).to.be.calledOnce;
+			render(<div id="a">new</div>, newScratch, newScratch.querySelector('#a'));
+			expect(newScratch.innerHTML).to.equal('<div id="a">new</div>');
+			expect(unmount).to.be.calledOnce;
+		});
+
 		it('should render multiple render roots in one parentDom', () => {
 			const childA = scratch.querySelector('#a');
 			const childB = scratch.querySelector('#b');