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Make middleware API dispatch pass through all call arguments #2560

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Aug 15, 2017
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Make middleware API dispatch pass through all call arguments #2560

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2 changes: 1 addition & 1 deletion src/applyMiddleware.js
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ export default function applyMiddleware(...middlewares) {

const middlewareAPI = {
getState: store.getState,
dispatch: (action) => dispatch(action)
dispatch: (...args) => dispatch(...args)
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why not just return dispatch?

const middlewareAPI = {
  getState: store.getState,
  dispatch,
}

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Hey! Can someone have an explanation for this change?

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@FranciscoMSM This particular change is to allow middleware to change the arguments of dispatch and pass that through.

The reason for the extra function is to remove direct access to dispatch so middleware doesn't try to attach properties or other hidden metadata to it. Each middleware gets its own unique copy of dispatch this way, and there is less chance of interference between middlewares.

}
chain = middlewares.map(middleware => middleware(middlewareAPI))
dispatch = compose(...chain)(store.dispatch)
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20 changes: 20 additions & 0 deletions test/applyMiddleware.spec.js
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,26 @@ describe('applyMiddleware', () => {
})
})

it('passes through all arguments of dispatch calls from within middleware', () => {
const spy = jest.fn()
const testCallArgs = ['test']
function multiArgMiddleware() {
return next => (action, callArgs) => {
if (Array.isArray(callArgs)) {
return action(...callArgs)
}
return next(action)
}
}
function dummyMiddleware({ dispatch }) {
return next => action => dispatch(action, testCallArgs)
}

const store = createStore(reducers.todos, applyMiddleware(multiArgMiddleware, dummyMiddleware))
store.dispatch(spy)
expect(spy.mock.calls[0]).toEqual(testCallArgs)
})

it('keeps unwrapped dispatch available while middleware is initializing', () => {
// This is documenting the existing behavior in Redux 3.x.
// We plan to forbid this in Redux 4.x.
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