Merge pull request #131 from balloob/dont-allow-dispatch-while-dispatch

Raise error if trying to dispatch from observer

Author: bhamodi

src/reactor.js

@@ -52,6 +52,9 @@ class Reactor {
     this.__batchDepth = 0
     // number of dispatches in the top most batch cycle
     this.__batchDispatchCount = 0
+
+    // keep track if we are currently dispatching
+    this.__isDispatching = false
   }
 
   /**
@@ -105,13 +108,22 @@ class Reactor {
    * @param {object|undefined} payload
    */
   dispatch(actionType, payload) {
+    if (this.__batchDepth === 0) {
+      if (this.__isDispatching) {
+        this.__isDispatching = false
+        throw new Error('Dispatch may not be called while a dispatch is in progress')
+      }
+      this.__isDispatching = true
+    }
+
     var prevState = this.state
     this.state = this.__handleAction(prevState, actionType, payload)
 
     if (this.__batchDepth > 0) {
       this.__batchDispatchCount++
     } else if (this.state !== prevState) {
       this.__notify()
+      this.__isDispatching = false
     }
   }
 
@@ -285,7 +297,10 @@ class Reactor {
 
     if (this.__batchDepth <= 0) {
       if (this.__batchDispatchCount > 0) {
+        // set to true to catch if dispatch called from observer
+        this.__isDispatching = true
         this.__notify()
+        this.__isDispatching = false
       }
       this.__batchDispatchCount = 0
     }

tests/reactor-tests.js

@@ -179,6 +179,25 @@ describe('Reactor', () => {
 
         expect(mockFn.calls.count()).toEqual(0)
       })
+
+      it('should raise an error if already dispatching another action', () => {
+        reactor.observe([], state => reactor.dispatch('noop', {}))
+
+        expect(() => checkoutActions.setTaxPercent(5)).toThrow(
+          new Error('Dispatch may not be called while a dispatch is in progress'))
+      })
+
+      it('should keep working after it raised for dispatching while dispatching', () => {
+        var unWatchFn = reactor.observe([], state => reactor.dispatch('noop', {}))
+
+        expect(() => checkoutActions.setTaxPercent(5)).toThrow(
+          new Error('Dispatch may not be called while a dispatch is in progress'))
+
+        unWatchFn()
+
+        expect(() => checkoutActions.setTaxPercent(5)).not.toThrow(
+          new Error('Dispatch may not be called while a dispatch is in progress'))
+      })
     }) // when dispatching a relevant action
 
     describe('#observe', () => {
@@ -1013,5 +1032,39 @@ describe('Reactor', () => {
       expect(observeSpy.calls.count()).toBe(1)
       expect(firstCallArg).toEqual(['one', 'two', 'three'])
     })
+
+    it('should not allow dispatch to be called from an observer', () => {
+      reactor.observe([], state => reactor.dispatch('noop', {}))
+
+      expect(() => {
+        reactor.batch(() => {
+          reactor.dispatch('add', 'one')
+          reactor.dispatch('add', 'two')
+        })
+      }).toThrow(
+        new Error('Dispatch may not be called while a dispatch is in progress'))
+    })
+
+    it('should keep working after it raised for dispatching while dispatching', () => {
+      var unWatchFn = reactor.observe([], state => reactor.dispatch('noop', {}))
+
+      expect(() => {
+        reactor.batch(() => {
+          reactor.dispatch('add', 'one')
+          reactor.dispatch('add', 'two')
+        })
+      }).toThrow(
+        new Error('Dispatch may not be called while a dispatch is in progress'))
+
+      unWatchFn()
+
+      expect(() => {
+        reactor.batch(() => {
+          reactor.dispatch('add', 'one')
+          reactor.dispatch('add', 'two')
+        })
+      }).not.toThrow(
+        new Error('Dispatch may not be called while a dispatch is in progress'))
+    })
   })
 })