Follow up: make new warning less wordy

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

@@ -215,11 +215,9 @@ describe('ReactComponentLifeCycle', () => {
  ReactTestUtils.renderIntoDocument(<StatefulComponent />);
  }).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 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.',
+ 'This is a no-op, but it might indicate a bug in your application. ' +
+ 'Instead, assign to `this.state` directly or define a `state = {};` ' +
+ 'class property with the desired state in the StatefulComponent component.',
  );
 
  // Check deduplication; (no extra warnings should be logged).

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

@@ -239,11 +239,9 @@ describe('ReactCompositeComponent', () => {
  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.',
+ 'This is a no-op, but it might indicate a bug in your application. ' +
+ 'Instead, assign to `this.state` directly or define a `state = {};` ' +
+ 'class property with the desired state in the MyComponent component.',
  );
 
  // No additional warning should be recorded
@@ -265,11 +263,9 @@ describe('ReactCompositeComponent', () => {
  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.',
+ 'This is a no-op, but it might indicate a bug in your application. ' +
+ 'Instead, assign to `this.state` directly or define a `state = {};` ' +
+ 'class property with the desired state in the MyComponent component.',
  );
 
  // No additional warning should be recorded

packages/react/src/ReactNoopUpdateQueue.js

@@ -22,14 +22,11 @@ function warnNoop(publicInstance, callerName) {
  warning(
  false,
  "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.',
+ 'This is a no-op, but it might indicate a bug in your application. ' +
+ 'Instead, assign to `this.state` directly or define a `state = {};` ' +
+ 'class property with the desired state in the %s component.',
  callerName,
  componentName,
- componentName,
  );
  didWarnStateUpdateForUnmountedComponent[warningKey] = true;
  }