Remove unused mount check in createContext (-6 B) (#2039)

The mount check in Provider sCU was redundant because renderComponent already checks a component is mounted before attempting to rerender it. Further whenever a consumer is unmounted we remove it from the sub list.

hooks/test/browser/useContext.test.js

@@ -242,4 +242,49 @@ describe('useContext', () => {
 			done();
 		});
 	});
+
+	it('should not rerender consumers that have been unmounted', () => {
+		const context = createContext(0);
+		const Provider = context.Provider;
+
+		const Inner = sinon.spy(() => {
+			const value = useContext(context);
+			return <div>{value}</div>;
+		});
+
+		let toggleConsumer;
+		let changeValue;
+		class App extends Component {
+			constructor() {
+				super();
+
+				this.state = { value: 0, show: true };
+				changeValue = value => this.setState({ value });
+				toggleConsumer = () => this.setState(({ show }) => ({ show: !show }));
+			}
+			render(props, state) {
+				return (
+					<Provider value={state.value}>
+						<div>{state.show ? <Inner /> : null}</div>
+					</Provider>
+				);
+			}
+		}
+
+		render(<App />, scratch);
+		expect(scratch.innerHTML).to.equal('<div><div>0</div></div>');
+		expect(Inner).to.have.been.calledOnce;
+
+		act(() => changeValue(1));
+		expect(scratch.innerHTML).to.equal('<div><div>1</div></div>');
+		expect(Inner).to.have.been.calledTwice;
+
+		act(() => toggleConsumer());
+		expect(scratch.innerHTML).to.equal('<div></div>');
+		expect(Inner).to.have.been.calledTwice;
+
+		act(() => changeValue(2));
+		expect(scratch.innerHTML).to.equal('<div></div>');
+		expect(Inner).to.have.been.calledTwice;
+	});
 });

src/create-context.js

@@ -2,10 +2,6 @@ import { enqueueRender } from './component';
 
 export let i = 0;
 
-/**
- *
- * @param {any} defaultValue
- */
 export function createContext(defaultValue) {
 	const ctx = {};
 
@@ -25,11 +21,8 @@ export function createContext(defaultValue) {
 				this.shouldComponentUpdate = _props => {
 					if (props.value !== _props.value) {
 						subs.some(c => {
-							// Check if still mounted
-							if (c._parentDom) {
-								c.context = _props.value;
-								enqueueRender(c);
-							}
+							c.context = _props.value;
+							enqueueRender(c);
 						});
 					}
 				};

test/browser/createContext.test.js

@@ -453,7 +453,7 @@ describe('createContext', () => {
 			app.setState({ status: 'updated' });
 			rerender();
 		});
-		
+
 		expect(scratch.innerHTML).to.equal('<p>value: updated</p>');
 	});
 
@@ -496,6 +496,54 @@ describe('createContext', () => {
 		expect(scratch.innerHTML).to.equal('<div>1</div>');
 	});
 
+	it('should not rerender consumers that have been unmounted', () => {
+		const { Provider, Consumer } = createContext(0);
+
+		const Inner = sinon.spy(props => <div>{props.value}</div>);
+
+		let toggleConsumer;
+		let changeValue;
+		class App extends Component {
+			constructor() {
+				super();
+
+				this.state = { value: 0, show: true };
+				changeValue = value => this.setState({ value });
+				toggleConsumer = () => this.setState(({ show }) => ({ show: !show }));
+			}
+			render(props, state) {
+				return (
+					<Provider value={state.value}>
+						<div>
+							{state.show ? (
+								<Consumer>{data => <Inner value={data} />}</Consumer>
+							) : null}
+						</div>
+					</Provider>
+				);
+			}
+		}
+
+		render(<App />, scratch);
+		expect(scratch.innerHTML).to.equal('<div><div>0</div></div>');
+		expect(Inner).to.have.been.calledOnce;
+
+		changeValue(1);
+		rerender();
+		expect(scratch.innerHTML).to.equal('<div><div>1</div></div>');
+		expect(Inner).to.have.been.calledTwice;
+
+		toggleConsumer();
+		rerender();
+		expect(scratch.innerHTML).to.equal('<div></div>');
+		expect(Inner).to.have.been.calledTwice;
+
+		changeValue(2);
+		rerender();
+		expect(scratch.innerHTML).to.equal('<div></div>');
+		expect(Inner).to.have.been.calledTwice;
+	});
+
 	describe('class.contextType', () => {
 		it('should use default value', () => {
 			const ctx = createContext('foo');