Bail out if stateProps can be calculated early and did not change

Fixes #1437, #300

Author: gaearon

src/components/connect.js

@@ -219,6 +219,7 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
         this.mergedProps = null
         this.haveOwnPropsChanged = true
         this.hasStoreStateChanged = true
+        this.haveStatePropsBeenPrecalculated = false
         this.renderedElement = null
         this.finalMapDispatchToProps = null
         this.finalMapStateToProps = null
@@ -229,13 +230,21 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
           return
         }
 
-        const prevStoreState = this.state.storeState
         const storeState = this.store.getState()
+        const prevStoreState = this.state.storeState
+        if (pure && prevStoreState === storeState) {
+          return
+        }
 
-        if (!pure || prevStoreState !== storeState) {
-          this.hasStoreStateChanged = true
-          this.setState({ storeState })
+        if (pure && !this.doStatePropsDependOnOwnProps) {
+          if (!this.updateStatePropsIfNeeded()) {
+            return
+          }
+          this.haveStatePropsBeenPrecalculated = true
         }
+
+        this.hasStoreStateChanged = true
+        this.setState({ storeState })
       }
 
       getWrappedInstance() {
@@ -251,11 +260,13 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
         const {
           haveOwnPropsChanged,
           hasStoreStateChanged,
+          haveStatePropsBeenPrecalculated,
           renderedElement
         } = this
 
         this.haveOwnPropsChanged = false
         this.hasStoreStateChanged = false
+        this.haveStatePropsBeenPrecalculated = false
 
         let shouldUpdateStateProps = true
         let shouldUpdateDispatchProps = true
@@ -269,7 +280,9 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
 
         let haveStatePropsChanged = false
         let haveDispatchPropsChanged = false
-        if (shouldUpdateStateProps) {
+        if (haveStatePropsBeenPrecalculated) {
+          haveStatePropsChanged = true
+        } else if (shouldUpdateStateProps) {
           haveStatePropsChanged = this.updateStatePropsIfNeeded()
         }
         if (shouldUpdateDispatchProps) {

test/components/connect.spec.js

@@ -1082,7 +1082,6 @@ describe('React', () => {
       )
       spy.destroy()
 
-
       spy = expect.spyOn(console, 'error')
       TestUtils.renderIntoDocument(
         <ProviderMock store={store}>
@@ -1547,6 +1546,51 @@ describe('React', () => {
       expect(renderCalls).toBe(1)
     })
 
+    it('should bail out early if mapState does not depend on props', () => {
+      const store = createStore(stringBuilder)
+      let renderCalls = 0
+      let mapStateCalls = 0
+
+      @connect(state => {
+        mapStateCalls++
+        return state === 'aaa' ? { change: 1 } : {}
+      })
+      class Container extends Component {
+        render() {
+          renderCalls++
+          return <Passthrough {...this.props} />
+        }
+      }
+
+      TestUtils.renderIntoDocument(
+        <ProviderMock store={store}>
+          <Container />
+        </ProviderMock>
+      )
+
+      expect(renderCalls).toBe(1)
+      expect(mapStateCalls).toBe(1)
+
+      const spy = expect.spyOn(Container.prototype, 'setState').andCallThrough()
+
+      store.dispatch({ type: 'APPEND', body: 'a' })
+      expect(mapStateCalls).toBe(2)
+      expect(renderCalls).toBe(1)
+      expect(spy.calls.length).toBe(0)
+
+      store.dispatch({ type: 'APPEND', body: 'a' })
+      expect(mapStateCalls).toBe(3)
+      expect(renderCalls).toBe(1)
+      expect(spy.calls.length).toBe(0)
+
+      store.dispatch({ type: 'APPEND', body: 'a' })
+      expect(mapStateCalls).toBe(4)
+      expect(renderCalls).toBe(2)
+      expect(spy.calls.length).toBe(1)
+
+      spy.destroy()
+    })
+
     it('should allow providing a factory function to mapStateToProps', () => {
       let updatedCount = 0
       let memoizedReturnCount = 0