As far as I know and correct me if I am wrong, redux-thunk is a middleware which helps us dispatch async function and debug values in the action itself while when I used redux-promise I couldn't create async functions without implementing my own mechanism as Action throws an exception of dispatching only plain objects.
What is the major differences between these two packages? Are there any benefits of using both the packages in a single page react app or sticking to redux-thunk would be enough?
redux-thunk allows your action creators to return a function :
function myAction(payload){
return function(dispatch){
// use dispatch as you please
}
}
redux-promise allows them to return a promise :
function myAction(payload){
return new Promise(function(resolve, reject){
resolve(someData); // redux-promise will dispatch someData
});
}
Both libraries are useful if you need to dispatch action async or conditionally. redux-thunk also allows you to dispatch several times within one action creator. Whether you choose one, the other or both entirely depends on your needs/style.
You'll likely want/need both together in your app. Start with redux-promise for routine promise-producing async tasks and then scale up to add Thunks (or Sagas, etc.) as complexity increases:
When life is simple, and you're just doing basic async work with creators that return a single promise, then redux-promise will improve your life and simplify that, quick and easy. (In a nutshell, instead of you needing to think about 'unwrapping' your promises when they resolve, then writing/dispatching the results, redux-promise(-middleware) takes care of all that boring stuff for you.)
But, life gets more complex when:
Maybe your action creator wants to produce several promises, which you want to dispatch as separate actions to separate reducers?
Or, you have some complex pre-processing and conditional logic to manage, before deciding how and where to dispatch the results?
In those cases, the benefit of redux-thunk is that it allows you to encapsulate complexity inside your action-creator.
But note that if your Thunk produces and dispatches promises, then you'll want to use both libraries together:
the Thunk would compose the original action(s) and dispatch them
redux-promise would then handle unwrapping at the reducer(s) the individual promise(s) generated by your Thunk, to avoid the boilerplate that entails. (You could instead do everything in Thunks, with promise.then(unwrapAndDispatchResult).catch(unwrapAndDispatchError)... but why would you?)
Another simple way to sum up the difference in use-cases: the beginning vs. the end of the Redux action cycle:
Thunks are for the beginning of your Redux flow: if you need to create a complex action, or encapsulate some gnarly action-creation
logic, keeping it out of your components, and definitely out of reducers.
redux-promise is for the end of
your flow, once everything has been boiled down to simple promises, and you just want to unwrap them and store their resolved/rejected value in the store
NOTES/REFS:
I find redux-promise-middleware to be a more complete and understandable implementation of the idea behind the original redux-promise. It's under active development, and is also nicely complemented by redux-promise-reducer.
there are additional similar middlewares available for composing/sequencing your complex actions: one very popular one is redux-saga, which is very similar to redux-thunk, but is based on the syntax of generator functions. Again, you'd likely use it in conjunction with redux-promise, because sagas produce promises you don't want to have to unwrap and process manually with tons of boilerplate...
Here's a great article directly comparing various async composition options, including thunk and redux-promise-middleware. (TL;DR: "Redux Promise Middleware reduces boilerplate pretty dramatically vs some of the other options" ... "I think I like Saga for more complex applications (read: "uses"), and Redux Promise Middleware for everything else.")
Note that there's an important case where you may think you need to dispatch multiple actions, but you really don't, and you can keep simple things simple. That's where you just want multiple reducers to react to a single async call, and you would be inclined to dispatch multiple actions to those multiple reducers. But, there's no reason at all why multiple reducers can't monitor a single action type. You'd simply want to make sure that your team knows you're using that convention, so they don't assume only a single reducer (with a related name) can handle a given action.
Full disclosure: I'm relatively new to Redux development and struggled with this question myself. I'll paraphrase the most succinct answer I found:
ReduxPromise returns a promise as the payload when an action is dispatched, and then the ReduxPromise middleware works to resolve that promise and pass the result to the reducer.
ReduxThunk, on the other hand, forces the action creator to hold off on actually dispatching the action object to the reducers until dispatch is called.
Here's a link to the tutorial where I found this info: https://blog.tighten.co/react-101-part-4-firebase.
Related
I am kind of in dilemma when do we need to use redux actions and redux saga actions.
I don't mean to ask when to use redux and when to use redux-saga. But I would like to know that what scenario do we need to use redux actions when we use redux saga. Or don't I need to use redux actions when using redux saga?
Please help me understanding the use cases of redux when using redux-saga.
Not sure if this is what you meant, but just in case: the actions themselves are indistinguishable between redux and redux-saga. In both cases, an action is an object with a type, and possibly a payload. For example, this is an action:
{
type: 'DO_STUFF',
value: 3,
}
When you dispatch an action, it's first going to go into your middlewares. Redux-saga is an example of a middleware, and it can decide whether it wants to do anything with the action. If the action gets past redux-saga, it then goes to the reducers.
So i believe what you're asking is: when should you handle an action with a saga, and when should you handle it with a reducer. The answer to that comes down to the reason redux-saga and similar middleware were created in the first place:
Reducers are always synchronous pure functions.
So you'll use a saga when you want to do something asynchronous and/or impure. The asynchronous part of that is the thing that comes up most often. If you want to fetch data, it will be in a saga. If you want to set up an interval to do something over time, it will be in a saga.
On rare occasions you might have something that's synchronous, but impure, and that might also be something you put in a saga. One recent example i had was that i wanted to dispatch an action, and rather than updating the application state, i wanted it to save something to local storage. This happens synchronously, but since it's a side effect it's better for me to put it in a saga.
As requested in the comments, a clarification about synchronous but impure. A function is synchronous if it does all its work before it returns. A function is pure if it 1) has no side effects and 2) for a given input, it always returns the same output.
A side effect is when a function changes something external to itself, but by a means other than its return value. With a pure function, i should be able to call it and assume that nothing has changed outside of that function. For example:
localStorage.setItem('data', 'hello world');
doSomething();
console.log(localStorage.getItem('data'));
If i know nothing about doSomething except that it's pure, then i can be certain that localStorage.getItem('data') will return 'hello world'. But on the other hand if doSomething is impure, then i can't make that assumption. In principle, the value in local storage could have been changed, resulting in a different log statement.
So a function that modifies local storage, such as the following, is impure despite being synchronous:
const doSomething = (value) => {
localStorage.setItem('data', value);
}
The second way something could be impure is if it doesn't always return the same thing for its same inputs. For example, the following function is synchronous but impure:
const getTime = () => {
return Date.now();
}
If i call that multiple times, i will usually get different numbers each time.
Both Redux Thunk and Redux Saga are middleware of Redux. What is the difference between two and how to determine when to use Redux Thunk or Redux Saga?
Both Redux Thunk and Redux Saga take care of dealing with side effects.
In very simple terms, applied to the most common scenario (async functions, specifically AJAX calls) Thunk allows Promises to deal with them, Saga uses Generators.
Thunk is simple to use and Promises are familiar to many developers, Saga/Generators are more powerful but you will need to learn them.
When Promises are just good enough, so is Thunk, when you deal with more complex cases on a regular basis, Saga gives you better tools.
As an example, what happens when you start an AJAX call in a route/view and then the user moves to a different one? Can you safely let the reducer change the state anyway? Saga makes it trivial to cancel the effect, Thunk requires you to take care of it, with solutions that don't scale as nicely.
In practical terms choosing one or the other one really depends (tautologically) on the project.
One thing to keep in mind is that the two middlewares can coexist, so you can start with Thunks and introduce Sagas when/if you need them (and then choose how/what to refactor with hands on experience... A solution that especially fits "learning projects", MVPs, et similia)
In general terms, Sagas are more powerful and easier to test, but they introduce many new concepts, that can be a bit overwhelming if you're also learning other technologies (Redux especially).
Specifically, while dealing with the simple and effective Redux philosophy (actions (literal objects) fed into reducers (pure functions)), you can deal with side effects with Thunk that is more limited but easy to grasp (Promise.then().error()), or with Saga that requires you to face the (powerful) notion that you can do more complex things with those actions.
It's also worth mentioning (redux-)observable has an even more complex (and even more powerful) paradigm to deal with side effects, just in case you are unfamiliar with it (if you already are, it might be easier to use than learning Saga).
Actually, Both of them are middleware for Redux to deal with asynchronous actions. For knowing the difference between then please pay attention to the following picture:
The middleware box generally refers to software services that glue together separate features in existing software. For Redux, middleware provides a third-party extension point between dispatching an action and handing the action off to the reducer. then reducer makes the new state.
Redux Thunk is a middleware that lets you call action creators that return a function instead of an action object. That function receives the store’s dispatch method, which is then used to dispatch regular synchronous actions inside the body of the function once the asynchronous operations have completed. simple, easy to learn and use with 352B volume
Redux Saga leverages an ES6 feature called Generators, allowing us to write asynchronous code that looks synchronous, and is very easy to test. In the saga, we can test our asynchronous flows easily and our actions stay pure. complicated, hard to learn and understand, 14kB volume but organized complicated asynchronous actions easily and make then very readable and the saga has many useful tools to deal with asynchronous actions
HINT: If you cannot understand the difference between them or understand the redux-saga flow but still you wanna have readable code and avoid callback hell, go after redux-thunk by using async/await, I leave an example for offer:
// simple usage of redux-thunk:
export const asyncApiCall = values => {
return dispatch => {
return axios.get(url)
.then(response =>{
dispatch(successHandle(response));
})
.catch(error => {
dispatch(errorHandle(error));
});
};
};
// async/await usage of redux-thunk:
export const asyncApiCall = values => {
return async dispatch => {
try {
const response = await axios.get(url);
dispatch(successHandle(response));
}
catch(error) {
dispatch(errorHandle(error));
}
};
};
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Why use Redux Thunk then one can do something like this:
ReadableAPI.getCategories().then((categories)=>{
console.log('after getCategories', categories)
this.props.dispatch(addCategories(categories))
})
Isn't this more straightforward and achieves the same thing?
This answer from Dan Abramov explains beautifully why you would want to use redux-thunk in your application. One more benefit of using redux-thunk in your application is that you keep your business logic separate from your view part (React in your case). We had a use case where our app was written in backbone and we wanted to re-write our whole app in React. We realised that it is easy if your view and collection/models are separate. We started depreciating just the html templates and not the collections. When we deprecated all the html templates, we started using Redux in our app and deprecated our collections too.
What I want to put here is that we had our view and business logic separate, we could refactor that easily. Similarly, with React and Redux, you would want to keep that different, so that if something new comes and replaces Redux, at least you won't have to deprecate your views and you just will have to change your business logic.
Redux Thunk basically allows us to delay the dispatch of an action, i.e we can handle the action returned by the action creator and call the dispatch function when we really want to dispatch.
Your example is incomplete and it was frustrating to follow how you arrived at that oversimplified solution. After researching it I realized, you probably have some ReadableAPI.js file somewhere you should have posted with what is probably a configuration using fetch and inside of it you probably have something like this:
export const getCategories = () =>
fetch('http://localhost:3001/categories', {headers})
.then(res => res.json())
.then(data => console.log(data))
which ties into your:
ReadableAPI.getCategories().then((categories)=>{
console.log('after getCategories', categories)
this.props.dispatch(addCategories(categories))
})
So in this solution you are returning a Promise which is an object which essentially gives us notification when some amount of work such as a network request is completed and in order to get notified we chain on the .then() function which we pass an arrow function like you did: then((categories)=> and that arrow function will be called at some point in the future.
It looks like you are referring to that data as categories and you are console logging 'after Categories', categories.
What we need to know is what are the different properties attached to that categories object? Does it have a data property? Does it have a results property with some actual data in it? Is there a categories.data.results that contains whatever the data is?
So let's just say the answer is yes to all the questions.
You are going about that in a bit of a hard way in order to deal with asynchronous requests because it's not just that snippet of code: there is also what's inside the ReadableAPI.js file, right? Also, you are using Promises that can get kind of hairy and you would have already put together two files just to deal with asynchronous request which would be okay if it was just a plain Reactjs application, but you mentioned your approach as an alternative to Redux-Thunk which implies using Redux.
For your approach in the vanilla Reactjs space I would use Axios and implement the async/await syntax, but with Redux involved you don't want to use a Promise.
Now, the action creator I had to make up in the ReadableAPI.js file would not work in a Redux environment because it does not return a plain JavaScript action object and so we would have to use a custom middleware as the error says to do.
So how does a middleware like Redux-Thunk work? Redux-Thunk essentially relaxes the rules around an action creator.
The purpose of Redux-Thunk is not to be passed a request object and it will take it away and go to work for you.
Redux-Thunk is an all purpose middleware that allows us to deal with asynchronous action creators, but it also allows us to do many other things as well.
With Redux Thunk involved, your action creator can return an action object. If you return an action object it still must have a type property and if it is an action object that gets returned it can optionally have a payload as well.
The other thing that Redux-Thunk does is allow you to return either an action object or a function.
If you return a function, Redux-Thunk will automatically call that function for you.
That's it, thats all Redux-Thunk does. However, One thing Redux-Thunk does really well is to manually dispatch an action. That is the key part. With Redux-Thunk we can manually dispatch an action at some point in time in the future.
So we get this new action created and it can be a plain JavaScript object or a function, but when we are dispatching it manually inside of Redux-Thunk or inside of a function it's basically always going to be a plain object.
So we will dispatch this action and it will flow back into dispatch and dispatch will send it right back into Redux-Thunk and Redux-Thunk will ask if it's an action or object.
When it's an object, Redux-Thunk forwards it automatically to all the different reducers.
With Redux-Thunk we can return a function and if we do, that function gets invoked with dispatch and getState arguments and with those two functions we have unlimited power over our Redux store and we can change any data and read any data and at any point in time in the future we can manually dispatch an action and update the data inside of our store.
Where am I getting the dispatch and getState? From the Redux-Thunk library source code:
https://github.com/reduxjs/redux-thunk/blob/master/src/index.js
src/index.js:
function createThunkMiddleware(extraArgument) {
return ({ dispatch, getState }) => next => action => {
if (typeof action === 'function') {
return action(dispatch, getState, extraArgument);
}
return next(action);
};
}
const thunk = createThunkMiddleware();
thunk.withExtraArgument = createThunkMiddleware;
export default thunk;
If you look at the if conditional you see the body of the actual logic that is going on. Did you just dispatch an action? If so, is it a function? If it is, then Redux-Thunk is going to invoke that action with dispatch and getState.
If our action is not a function, Redux-Thunk does not care about it, so on it goes to the next middleware as indicated by the return next(action);, otherwise on to the reducers if there is no middleware to run.
I'm in a problem when update store of my react redux app.
How can I make store update thenable?
As you know, all updates of states are async, so we have to use componentDidUpdate method if I do something as a callback function of state update. But these are sometimes complicated. I'd like to make this simple, by something like making them thenable method. Does have any body any idea?
The reducer function supposed to be pure so the async logic should not be there.
There are few middlewares you might be interested in:
redux-thunk allows you to have action creator that returns a function which dispatch and getState from store are injected into a normal action which means can delay the dispatch however you want. But it has limited power. (which you might not need more than that)
redux-saga use generators to explain all the side-effects and async operation in terms of data. It is more powerful than thunk, you can do complicated async interaction, for example, racing between multiple actions. But the downside is there will be more action you need to create and unpredictability caused by action dependencies.
redux-observable is claimed to be more sophisticated than saga. It is based on Rx observable stream and you can manipulate stream of actions with map flatMap filter which similar to array's method but there are more you can use. For me, it's interface looks much nicer than saga. Some might argue against the learning curve needed for understanding Rx.
In my react / redux application I often want to dispatch multiple actions after another.
Given the following example: After a successful login I want to store the user data and after that I want to initiate another async action that loads application configuration from the server.
I know that I can use redux-thunkto build an action creator like this
function loginRequestSuccess(data) {
return function(dispatch) {
dispatch(saveUserData(data.user))
dispatch(loadConfig())
}
}
So my questions are:
When the first dispatchreturns, is the state already changed by all reducers listening for that action? I'm wondering if the two dispatch calls are run strictly sequential.
Is this approach considered best practice for dispatching multiple actions? If not, what would you suggest alternatively?
Thanks for any help!
Yes redux-thunk allows you to do as you say, and yes it is a best practice for dispatching multiple actions (one that I prefer over the alternatives because of it's simplicity). The state is indeed updated as soon as you dispatch (by the time it returns), which is why you are given a function to retrieve the state in a thunk, instead of simply a reference to the state. In that way you can alter the state with one dispatch, and then call getState() to get a reference to the new state to read from if you need to.
redux-thunk is exactly what you are looking for. I consider it very good practice.
To answer your question, indeed when the first dispatch returns the state is already changed by the called reducers.
I know its a late response :-P You can do this by using Redux-Thunk and also checkout Redux-Saga. Redux Saga provides an amazing way to handle loads of actions at the same time. Below is an example of dispatching multiple actions using Redux-Thunk
function getAndLoadSider(moduleName){
return function(dispatch){
return doSomeApiCall(someData).then(function(item){
let _item = someOtherFunction(item.collections);
let _menuData = {
name: item.name,
key: item.key
};
return new Promise(function(res, rej){
dispatch(actionOne(_menuData));
res(_item);
}).then((_item) => dispatch(actionTwo(_item)))
}
}
Above method works well for your case when one action is dependent on the first. This is a promise based approach. If you don't like to do a lots of Promise coding I recommend you go for Sagas. Check out this link https://redux-saga.js.org/docs/advanced/ComposingSagas.html where you will learn how to compose sagas. Learning curve is steep; but once you are done, Sagas will make you a ninja redux dev.
Hope this helps :-)