Improve not-yet-mounted setState warning

packages/react-dom/src/__tests__/ReactComponentLifeCycle-test.js

@@ -214,10 +214,12 @@ describe('ReactComponentLifeCycle', () => {
  expect(() => {
  ReactTestUtils.renderIntoDocument(<StatefulComponent />);
  }).toWarnDev(
- 'Warning: setState(...): Can only update a mounted or ' +
- 'mounting component. This usually means you called setState() on an ' +
- 'unmounted component. This is a no-op.\n\nPlease check the code for the ' +
- 'StatefulComponent component.',
+ "Warning: Can't call setState on a component that is not yet mounted. " +
+ 'This is a no-op, but it might indicate a bug in your application.\n\n' +
+ 'To fix, assign the initial state in the StatefulComponent constructor. ' +
+ 'If the state needs to reflect an external data source, ' +
+ 'you may also add a componentDidMount lifecycle hook to StatefulComponent ' +
+ 'and call setState there if the external data has changed.',
  );
 
  // Check deduplication; (no extra warnings should be logged).

packages/react-dom/src/__tests__/ReactCompositeComponent-test.js

@@ -225,6 +225,58 @@ describe('ReactCompositeComponent', () => {
  expect(inputProps.prop).not.toBeDefined();
  });
 
+ it('should warn about `forceUpdate` on not-yet-mounted components', () => {
+ class MyComponent extends React.Component {
+ constructor(props) {
+ super(props);
+ this.forceUpdate();
+ }
+ render() {
+ return <div />;
+ }
+ }
+
+ const container = document.createElement('div');
+ expect(() => ReactDOM.render(<MyComponent />, container)).toWarnDev(
+ "Warning: Can't call forceUpdate on a component that is not yet mounted. " +
+ 'This is a no-op, but it might indicate a bug in your application.\n\n' +
+ 'To fix, assign the initial state in the MyComponent constructor. ' +
+ 'If the state needs to reflect an external data source, ' +
+ 'you may also add a componentDidMount lifecycle hook to MyComponent ' +
+ 'and call setState there if the external data has changed.',
+ );
+
+ // No additional warning should be recorded
+ const container2 = document.createElement('div');
+ ReactDOM.render(<MyComponent />, container2);
+ });
+
+ it('should warn about `setState` on not-yet-mounted components', () => {
+ class MyComponent extends React.Component {
+ constructor(props) {
+ super(props);
+ this.setState();
+ }
+ render() {
+ return <div />;
+ }
+ }
+
+ const container = document.createElement('div');
+ expect(() => ReactDOM.render(<MyComponent />, container)).toWarnDev(
+ "Warning: Can't call setState on a component that is not yet mounted. " +
+ 'This is a no-op, but it might indicate a bug in your application.\n\n' +
+ 'To fix, assign the initial state in the MyComponent constructor. ' +
+ 'If the state needs to reflect an external data source, ' +
+ 'you may also add a componentDidMount lifecycle hook to MyComponent ' +
+ 'and call setState there if the external data has changed.',
+ );
+
+ // No additional warning should be recorded
+ const container2 = document.createElement('div');
+ ReactDOM.render(<MyComponent />, container2);
+ });
+
  it('should warn about `forceUpdate` on unmounted components', () => {
  const container = document.createElement('div');
  document.body.appendChild(container);

packages/react/src/ReactNoopUpdateQueue.js

@@ -21,12 +21,15 @@ function warnNoop(publicInstance, callerName) {
  }
  warning(
  false,
- '%s(...): Can only update a mounted or mounting component. ' +
- 'This usually means you called %s() on an unmounted component. ' +
- 'This is a no-op.\n\nPlease check the code for the %s component.',
- callerName,
+ "Can't call %s on a component that is not yet mounted. " +
+ 'This is a no-op, but it might indicate a bug in your application.\n\n' +
+ 'To fix, assign the initial state in the %s constructor. ' +
+ 'If the state needs to reflect an external data source, ' +
+ 'you may also add a componentDidMount lifecycle hook to %s ' +
+ 'and call setState there if the external data has changed.',
  callerName,
  componentName,
+ componentName,
  );
  didWarnStateUpdateForUnmountedComponent[warningKey] = true;
  }