Revive single text-child hot path

src/diff/index.js

@@ -486,7 +486,6 @@ function diffElementNodes(
 			}
 		}
 
-		// If the new vnode didn't have dangerouslySetInnerHTML, diff its children
 		if (newHtml) {
 			// Avoid re-applying the same '__html' if it did not changed between re-render
 			if (
@@ -499,6 +498,15 @@ function diffElementNodes(
 			}
 
 			newVNode._children = [];
+		} else if (
+			typeof newChildren === 'string' &&
+			typeof oldProps.children === 'string'
+		) {
+			if (newChildren !== oldProps.children) {
+				oldVNode._children[0]._dom.data = newChildren;
+				newVNode._children = oldVNode._children;
+				oldVNode._children = [];
+			}
 		} else {
 			if (oldHtml) dom.innerHTML = '';
 

test/browser/fragments.test.js

@@ -1325,6 +1325,7 @@ describe('Fragment', () => {
 		);
 	});
 
+	// TODO
 	it('should support moving Fragments between beginning and end', () => {
 		const Foo = ({ condition }) => (
 			<ol>
@@ -1392,8 +1393,10 @@ describe('Fragment', () => {
 			'rendering from false to true'
 		);
 		expectDomLogToBe([
-			'<ol>450123.appendChild(<li>4)',
-			'<ol>501234.appendChild(<li>5)'
+			'<ol>450123.insertBefore(<li>0, <li>4)',
+			'<ol>045123.insertBefore(<li>1, <li>4)',
+			'<ol>014523.insertBefore(<li>2, <li>4)',
+			'<ol>012453.insertBefore(<li>3, <li>4)'
 		]);
 	});
 

test/browser/keys.test.js

@@ -354,7 +354,7 @@ describe('keys', () => {
 		render(<List values={values} />, scratch);
 		expect(scratch.textContent).to.equal('abcd', 'swap back');
 		expect(getLog()).to.deep.equal(
-			['<ol>acbd.insertBefore(<li>c, <li>d)'],
+			['<ol>acbd.insertBefore(<li>b, <li>c)'],
 			'swap back'
 		);
 	});

test/browser/lifecycles/componentWillUnmount.test.js

@@ -68,5 +68,25 @@ describe('Lifecycle methods', () => {
 			render(<Foo />, scratch);
 			render(null, scratch);
 		});
+
+		it('should only remove dom after componentWillUnmount was called with single text child', () => {
+			class Foo extends Component {
+				componentWillUnmount() {
+					expect(document.getElementById('foo')).to.not.equal(null);
+				}
+
+				render() {
+					return <div id="foo" />;
+				}
+			}
+
+			render(
+				<div>
+					<Foo />
+				</div>,
+				scratch
+			);
+			render(<div>Text</div>, scratch);
+		});
 	});
 });

test/browser/placeholders.test.js

@@ -474,4 +474,16 @@ describe('null placeholders', () => {
 		expect(getLog()).to.deep.equal(['<div>Test3.remove()']);
 		expect(ref).to.have.been.calledOnce;
 	});
+
+	it('should properly mount and unmount text nodes with placeholders', () => {
+		function App({ show = false }) {
+			return <div>{show && 'Hello'}</div>;
+		}
+
+		render(<App show />, scratch);
+		expect(scratch.innerHTML).to.equal('<div>Hello</div>');
+
+		render(<App />, scratch);
+		expect(scratch.innerHTML).to.equal('<div></div>');
+	});
 });

test/browser/render.test.js

@@ -1676,10 +1676,10 @@ describe('render()', () => {
 		expect(getLog()).to.deep.equal([
 			'<div>.appendChild(#text)',
 			'<div>1352640.insertBefore(<div>11, <div>1)',
-			'<div>111352640.insertBefore(<div>1, <div>5)',
-			'<div>113152640.insertBefore(<div>6, <div>0)',
-			'<div>113152460.insertBefore(<div>2, <div>0)',
-			'<div>113154620.insertBefore(<div>5, <div>0)',
+			'<div>111352640.insertBefore(<div>3, <div>1)',
+			'<div>113152640.insertBefore(<div>4, <div>5)',
+			'<div>113145260.insertBefore(<div>6, <div>5)',
+			'<div>113146520.insertBefore(<div>2, <div>5)',
 			'<div>.appendChild(#text)',
 			'<div>113146250.appendChild(<div>9)',
 			'<div>.appendChild(#text)',
@@ -1813,4 +1813,37 @@ describe('render()', () => {
 			);
 		}
 	});
+
+	it('should correctly transition from multiple children to single text node and back', () => {
+		class Child extends Component {
+			componentDidMount() {}
+			componentWillUnmount() {}
+			render() {
+				return 'Child';
+			}
+		}
+
+		const proto = Child.prototype;
+		sinon.spy(Child.prototype, 'componentDidMount');
+		sinon.spy(Child.prototype, 'componentWillUnmount');
+
+		function App({ textChild = false }) {
+			return <div>{textChild ? 'Hello' : [<Child />, <span>b</span>]}</div>;
+		}
+
+		render(<App />, scratch);
+		expect(scratch.innerHTML).to.equal('<div>Child<span>b</span></div>');
+		expect(proto.componentDidMount).to.have.been.calledOnce;
+		expect(proto.componentWillUnmount).to.have.not.been.called;
+
+		render(<App textChild />, scratch);
+		expect(scratch.innerHTML).to.equal('<div>Hello</div>');
+		expect(proto.componentDidMount).to.have.been.calledOnce;
+		expect(proto.componentWillUnmount).to.have.been.calledOnce;
+
+		render(<App />, scratch);
+		expect(scratch.innerHTML).to.equal('<div>Child<span>b</span></div>');
+		expect(proto.componentDidMount).to.have.been.calledTwice;
+		expect(proto.componentWillUnmount).to.have.been.calledOnce;
+	});
 });