I've been reading about the advantages of using Context in React and I am unconvinced. I'm wondering if there's something I've missed.
Context provides a way to pass data through the component tree without having to pass props down manually at every level.
What's the hassle in creating a props object in the main component and just passing it around among the underlings? Something like:
// do this once at top level (I'm assuming [foo, foo_set] and [bar, bar_set] are state variables):
const props = {foo, foo_set, bar, bar_set, thisAndThat, theOther, whatever, etcAndEtc}
// including one component
<MyComponent1 {...props } />
// including another
<MyComponent2 {...props } />
(Maybe better to use another name than props for this object, as the components can have other properties. Anyway.)
Then in MyComponent1 you can access all the props you want, or not access them. Either:
...
const MyComponent1 = (props) => {
...
// here we can use any props we need, props.bar, props.bar_set, props.theOther for example
const localVar = props.bar * 2;
props.bar_set(localVar);
// this changes the value of bar throughout the app
...
}
the advantage of the above, as I see it, is that you can pass around the props object to other sub-sub-components and not worry about whether you have anything missing.
Or:
...
const MyComponent1 = ({bar, bar_set, theOther }) => {
...
// here we can use bar, bar_set, theOther in the same example
const localVar = bar * 2;
bar_set(localVar);
...
}
The advantage of this option being that the syntax is shorter.
So my point is why not just use the standard JavaScript syntax? Why introduce new concepts when there are plenty to assimilate to do all sorts of other things?
Consider a fairly common case for most applications: You have authentication information (eg, the current user), a routing library (eg, react-router), and a theme object (what colors to use). These are needed in components scattered throughout the app.
You want to render a button somewhere down at the tip of the component tree. It's going to show the user's avatar, so it needs the authentication data. It's going to navigate when clicked, so it needs the navigate function from the routing library. And it needs to style itself according to the theme.
This certainly can be done through props, but in order for the button to get the props, every component in the chain above it must get and forward those props too. This could be many components deep, like page component -> section component -> table -> row -> widget -> button, and most of them don't need that information for themselves, so they're just taking the props in order to forward it along.
And you can easily imagine cases where there are more than 3 pieces of data that are needed across the app.
What's the hassle
Most people find this "prop drilling" to be a hassle, but let's assume you don't. You still have the problem that it has bad performance. If every component must receive the full set of "global" values that the app might need, then any time anything changes, the entire app must rerender. Optimizations like react.memo become effectively useless. You will get much better performance if you only pass the props you need.
Easier to edit code (You don't have to delete for example unused variable)
Better redability (You dont see unnescesary variables, and You see which component is using variables)
Lesser performance waste (preventing from consuming unnescesarry variables)
Suppose You got 10 descendants in - You would have to pass one variable through 10 of components.
What if some could have the same variable name ? You would have to edit Your passed variable for a while, then edit back later.
To sum up:
Using Context more efficient than stuffing everything into a single object variable, because it avoids re-rendering the whole app when anything changes.
People think passing a single variable around is more hassle than introducing specific syntax.
Context also allows you to have different values for the same variable in different parts of the app. This is shown here (the best explanation IMHO) : https://beta.reactjs.org/learn/passing-data-deeply-with-context
The above article also specifies that sometimes passing props is the best solution. It gives a list of use cases for context, and the advantages provided in each case.
Related
I'm having a little bit of difficulty figuring out how to reuse components in many places.
Obviously the reason why react is so good is because you can create common components and reuse them across many different pages, or just multiple times in the same page.
I have this component for displaying a dropdown that a user can use to select a new value, and change their settings. This component is reused in many different places on my website.
<ChannelSelect
channelID={
saveEnabled.saveEnabled.newSettings.verificationPanel.channelID
}
settings={
saveEnabled.saveEnabled.newSettings.verificationPanel.channelID
}
/>
What I am struggling with is telling this component which key: value in the state (object) to change. This is because simply passing in the code below, doesn't actually allow me to change the state of this specific key.
settings={saveEnabled.saveEnabled.newSettings.verificationPanel.channelID}
In my select menus onChange event I have the code snippet below. However, this doesn't actually allow me to change the specific value declare, it would actually just overwrite the whole object.
const { saveEnabled, setSaveEnabled } = useContext(SaveContext);
const onChange = (event) => {
props.settings = "newValue"
setSaveEnabled(props.settings)
Any idea how I can do this?
I'm trying to make a scene graph in React that supports nesting components. Something along the lines of:
<SceneNode>
<SceneNode>
<Thing/>
</SceneNode>
<SceneNode>
<Thing/>
</SceneNode>
</SceneNode>
When a SceneNode is mounted I need a way for it to know at what "depth" it is. Is there a way within a component to access that information? e.g.:
function SceneNode({children}:{children:ReactNode}) {
const depth = useCallDepth(); // <- some magic function that lets me know the level of nesting for this node
return <div>{children}</div>
}
NOTE: I've tried the following:
Context: Can't get it to work without having each node create its own context but since context is referenced statically in React I can't access the dynamically created parent contexts from children.
Refs: The nesting of components should be reflected in the DOM elements they produce, but I can't figure out how to determine what the associated component is for a given DOM element - i.e. is this div a SceneNode or just a random div? (I suppose I could encode it in an attribute or id, but I was hoping for something a little cleaner and less invasive)
Manual: I can manually specify which nodes are parents (e.g. <SceneNode parent={true}/> but that's pretty error prone.
It is possible to use context for this: Demo
I recently use react hook well. however sometime I wonder my coding style is okay.
let mDown = false;
let timerId = null;
function App() {
useEffect(() => {
mDown = true
....
}, [])
}
Like bottom code, I declare variable out of function. and I want to use common variable and access, change this value without using state.
Is it anti-pattern?
Thanks to read. :)
yes, of course. you can use the common variable in not only the hook function, but also any other methods of the App.
however the best practice is to make the global variables in other js files like constant.js, and import them in the above of the file.
import { mDown, timerId } from '../constant'
So let's think in terms of components. I mean, let's ignore for a while there barely will be more than one <App /> but think about component-centric approach in general.
Do you mean some data independent for each component's instance? Then you use useState(if changing this data should re-render component) or useRef(if updating this should never trigger re-rendering).
Or should that data be shared among all the components? Then, again it depends. Sometimes global variable is fine(real global variable, as a property on window object), sometimes better to put it into Context API or any state management layer(Mobx, Redux) instead.
Why don't have module-level variable as you aer going to? I see multiple reasons(again, maybe not big deal for exact case with <App />):
Module-level variable sticks to module instance. If we you ever end with multiple version of the same component in the same application, they will have own instances of such a variable. Think of <Dropdown /> component and some variable made to collapse all other instances once some is expanded. In case with module-level variable you may end some dropdown closes some instances - but not all - just if you got few versions of the same package used(like coming as 2nd level dependency)
No access, and no isolation - hard to unit-test.
And finally: what could be a profit here?
Lately I've been trying to write my React components as "Pure Functions" and I've noticed that sometimes I want to have something which feels a lot like state. I was thinking about passing my state as a second parameter to my component. I can achieve this by calling my component as a normal function with two parameters, props and state.
For example:
// abstracted to it's own module
const useState = (Component, state = {}) => {
return class extends React.Component {
state = createState(this, state); // will traverse and update the state
render() {
const { props, state } = this;
return Component(props, state); // <-- call the Component directly
}
};
};
const Component = (props, { index, increase }) => (
<div onClick={increase} {...props}>
Click me to increase: {index}
</div>
);
const componentState = {
index: 0,
increase: (event, state) => ({ ...state, index: state.index + 1 })
};
const StatefullComponent = useState(Component, componentState);
<StatefullComponent style={{ color: "purple" }} />;
I have a CodeSandbox example:
My questions are:
Will this pattern harm performance?
I'm no longer extending the props with state values, this might be a good thing
I am messing with the way components are rendered by default, this might be a bad thing
Will this Pattern break things like shouldComponentUpdate? (I have a sinking feeling this is modelling the old context api)
How worried should I be that future react updates will break this code?
Is there a more "Reacty" way of using State in a Pure function without resorting to libraries like Redux?
Am I trying to solve something which should not be solved?
Note: I'm using state in this example, but it could also be a theme, authorisation rules or other things you might want passed into your component.
EDIT 19-03-2018: I have noticed that people seem to be confused about what I'm asking. I'm not looking for a new framework or a conversation about "why do you want to separate your concerns?". I am quite sure this pattern will clean up my code and make it more testable and "cleaner" in general. I really want to know if the React framework will in any way hinder this pattern.
At first glanced when I checked your code I had a question:
"Why do you make it so complicated? When you can simply make it with a class declaration".
But later when I have splitted your code I found it really worth to do that.
Question 1: Doesn't really make a difference, it is the way how HOC does the composition.
I'm no longer extending the props with state values, this might be a good thing
Why/When might it be a good thing?
I am messing with the way components are rendered by default, this might be a bad thing
I don't see that you break or mess the rendering by default, I think the HOC pattern promotes the same philosophy, the difference you separate state from props.
Question 2: If a developer decide to use a stateless component then he/she should realize all “lifecycle methods” or references ref will be not available.
Your pattern make stateless component as “statefull” but in stateless declaration - amazing 😋.
Like in JSX you write in JS an "HTML" and inside it JS code with another "HTML":
<ul>
{list.map(text => <li>text</li>)} // I know there should be used key
</ul>
Mr. Baudin pattern (state-full like stateless):
import React from 'react'
import {useState} from './lib'
const state = {
index: 0,
increase: (event, state) => ({index: state.index + 1})
}
const Component = (props, state) => (
<div onClick={state.increase} {...props}>
Click me to increase: {state.index}
</div>
)
export default useState(Component, state)
Question 3: It depends what break changes will be in coming versions.
Question 4: Well... I don't think the offered pattern (implemented library) can be considered as application state management but it can be used within any state management like Redux or Mobx because it deals with internal component state.
Question 5: No, I don't think. Your solution makes code less and clean. Functional components are good for very simple or representational components and now it can be extended with state.
While this question has been open I've done some painful research on the subject and I'd like to share this research with you.
Question 1: Performance; Calling your components as functions or even as constructor functions doesn't really make a difference. You simply get your component instead of a type.
// the component
const MyComponent = () => (<div>This is my page</div>);
console.log(MyComponent());
console.log(new MyComponent());
console.log(<MyComponent />);
console.log(React.createElement(MyComponent));
Pen (Don't forget to inspect the developer tools!)
What I've noticed is that when you call a component directly you lose a little information, for example, when I use JSX the type information is preserved:
React.createElement(MyComponent).type === MyComponent // <- true
MyComponent() // <- Now way to find out what constructed this...
This doesn't seem like a big deal because the MyComponent() is seen as a normal div so it should render correctly; but I can imagine that React might do some lookup on the type of the component and calling your function like this that might interfere with the performance.
Haven't found anything in the documentation nor in the source code to suggest that this is the case, so I see no reason to worry about performance at this point.
Question 2: Does this break shouldComponentUpdate; the answer is "maybe not", but not because I need to write a class as was suggested. The problem is that React does a shallow compare on the props when you use a PureComponent and with pure functions just expects that with the same props you get the same result. In my case, because of the second parameter it might think the component doesn't need to update but actually it should. Because of some magic in my implementation this seems to work for child components of a root component wrapped with the useState function.
This is as I expected the same problem as with the original implementation of the context api. And as such I should be able to solve it using some reactive techniques.
Question 3: Seeing how "just calling a component as a function" seems to be the entire idea behind react and seeing how it results in almost exactly the same component without the original type information I see no reason why this should break in the future.
Question 4/5: No, there is no more "Reacty" way of really solving this problem. There is how ever a more functional way. I could use a state monad and lift the entire thing up; but that would envolve a lot of work and I really can't see the benefit of doing that. Passing state as a second parameter seems, at least for now, as something which might be strange but viable and actually feasable.
Question 5: When I started looking around I didn't find a lot os answers to these questions, but now that I've really dug myself in I can see a few other libraries doing the same thing. For example: recompose which calls itself "lodash for react". They seem to use this pattern of wrapping your component in a function and returning a class a lot. (Their withState implementation).
Extra information: My conclusion is that this pattern (because it's nothing more than a pattern) is valid and does not break any fundamental rules of React. Just to give a little bit of extra information Bernardo Ferreira Bastos Braga wrote that I needed to use a class to do it "the React way". I fail to see how wrapping your function and returning a class with state is anything other than "using a class".
I do however realise that wrapping a function increases complexity, but not by much; function calls are really optimised and because you write for maintainability and optimise later.
One of my biggest fears is that when the software gets more and more complocated and we get more cross-cutting concerns to deal with, it will get harder and harder to handle every concern as a parameter. In this case it might be good to use a destructuring pattern to get the concerns which you need from a "concerns" obejct passed as the second parameter.
One last thing about this pattern. I've done a small test (Just selenium rendering a page a 100 times) and this pattern, on a small scale, is faster than using Redux. The bigger your redux state gets and the more components you connect the faster this pattern becomes. The down side is that you are now doing a bit of manual state management, this comes with a real cost in complexity. Just remember to weigh all options.
A few examples of why this state component
Applications which interact with users, require that you try to keep track of the interactions they have. These interactions can be modeled in different ways but I really like a stateful approach. This means that you 'thread' state through your application. Now in react you have a few ways of creating components. The three I want o mention are:
create a class and extend from Component
create a class and extend from PureComponent
create a stateless function
I really like the last option but, to be honest, it's a pain keeping your code performant. There are a lot of articles our there explaining how lambda expression will create a new function every time your component is called, breaking the shallow compare of the props done by PureComponent.
To counteract this I use a pattern where I wrap my stateless component in a HoC where I pass my component and my state object. This HoC does some magic and passes the state as a second parameter to the stateless function, ensuring that when the props are tested by the compare of the PureComponent it should work.
Now to make the wrapper even better I memoize the lambdas so that only a single reference to that function exists so that even if you were to test the function by reference it should still be OK.
The code I use for this is:
return Object.entries(_state).reduce(
(acc, entry) => {
const [key, value] = entry;
if (value instanceof Function) {
acc[key] = _.memoize(item => (...args) => {
const newState = value.apply(null, [...args, root.state, root.props]);
root.setState(newState);
});
} else {
acc[key] = value;
}
return acc;
},
{}
);
};
As you can see I memoize the function and call it proxying the arguments and passing in the state and the props. This works as long as you can call these functions with a unique object like so:
const MyComponent = useState((props, { items, setTitle }) => {
return (
<div>
{items.map(item => (
<Component key={item.id} item={item} changeItem={setTitle(item)} />
))}
</div>
);
}, state);
1- Will this pattern harm performance?
Performance is usually not a black/white, rather it is better / worse in different scenarios. Since React already has a standard way of doing this, it it plausible that you'll be missing out on internal optimizations.
2-Will this Pattern break things like shouldComponentUpdate? (I have a sinking feeling this is modelling the old context api)
Yes, you should be using the class declaration if you need to write shouldComponentUpdate functions
3- How worried should I be that future react updates will break this code?
I think is fair to say that you should, since there are obvious and documented ways of doing the same using classes.
4 - Is there a more "Reacty" way of using State in a Pure function without resorting to libraries like Redux?
you could have a container component that has state and pass down callback functions to update the state
5- Am I trying to solve something which should not be solved?
yes, since there is already a mainstream and documented way of archieving what you need using the Component class. You should probably resort to functional components only for very simple or presentational components
As I get further into implementing redux + react into a fairly complex app which depends on many API requests to load a single page, I'm having trouble deciding whether it's better to have a single container component at the root of the page which handles all async stuff and passes props down to dumb components, v.s. having multiple container components which concern themselves only with the data they need, as well as fetching the data they need. I've gone back and forth between these two patterns and found that they each have pros/cons:
If I put a single container component at the top:
pro: All isFetching props and fetchSomeDependency() actions can be handled in one place.
con: the downside which is really annoying is that I find myself having to forward props and callbacks through multiple components, and certain components in the middle of the tree end up being tied up to this.
Here's a visual example of the issue that shows the relationships required props-wise:
<MyContainer
data={this.props.data}
isFetchingData={this.props.isFetchingData}
fetchData={this.props.fetchData}
>
{!isFetchingData &&
<MyModal
someData={props.data}
fetchData={props.fetchData}
>
<MyModalContent
someData={props.data}
fetchData={props.fetchData}
>
<SomethingThatDependsOnData someData={props.someData} />
<SomeButtonThatFetchesData onClick={props.fetchData} />
</MyModalContent>
</MyModal>
}
</MyContainer>
As you can see, <MyModal /> and <MyModalContent /> now need to be concerned with props that have nothing to do with it, seeing as a modal should be able to be re-used and only be concerned with stylistic qualities of a modal.
At first the above seemed great but once I got to 100+ components it all felt very tangled, and I found the complexity of these top-level container components to be too high for my liking, seeing as most of them (in the app I'm working on) depend on responses from 3+ API requests.
Then I decided to try multiple containers:
pro: Completely removes the need to forward props. It still makes sense to do it in some cases, but it's a lot more flexible.
pro: Way easier to refactor. I'm surprised at how I can significantly move around and refactor components without anything breaking, whereas in the other pattern things broke a lot.
pro: The complexity of each container component is much less. My mapStateToProps and mapDispatchToProps is more specific to the purpose of the component it's in.
con: Any component that depends on async stuff will always need to handle isFetching state in itself. This adds complexity that is not necessary in the pattern where its handled in a single container component.
So the main dilemma is that if I use one container, I get this un-necessary complexity in components between the root container and the leaf components. If I use multiple containers, I get more complexity in the leaf components, and end up with buttons that need to worry about isFetching even though a button should not be concerned about that.
I'd like to know if anyone has found a way to avoid both cons, and if so, what is the "rule of thumb" you follow to avoid this?
Thanks!
The way I have always seen it is to have your containers at the top most component of a logical components group other than your root/app component.
So if we have a simple search app that display results and lets assume the component heiarchy is such
<Root> <- setup the app
<App>
<Search/> <- search input
<Results/> <- results table
</App>
</Root>
I would make Search and Results redux aware containers. Because react component are suppose to be composable. You might have other components or pages that need display Results or Search. If you delegate the data fetch and store awareness to the root or app component, it make the components become dependent on each other/app. This make it harder down the line when you have to implement changes, now you have to change all the places that use them.
The exception to this is probably if you do have really tightly coupled logic between components. Even then, I would say then you should create a container that wraps your tightly coupled components since they won't be abled to be used realistically without each other.
Redux author Dan Abramov suggests that you use container components when you need them. That is, once you get to have too many props wiring up and down between components it's time to use containers.
He calls it an "ongoing process of refactoring".
See this article: https://medium.com/#dan_abramov/smart-and-dumb-components-7ca2f9a7c7d0
I wouldn't even consider using a single container approach. It pretty much entirely negates all advantages of redux. There is no need whatsoever to have a state management system if all your state is in one place and all your callbacks are in one place (root component).
I think there's a thin line to walk, though. I'm making an app where I've been at it for about 5 weeks (part time) and it's up to 3000 lines right now. It has 3 levels of view nesting, a routing mechanism i implemented myself, and components that are 10+ levels of nesting deep that need to modify state. I basically have one redux container for each big screen and it works marvelously.
However, if I click on my "clients" view, I get a clients listing which is fine, since my clients view is inside a redux container and gets the list of clients passed as props. However, when I click on one client, I'm really hesitant to do another redux container for the individual client's profile since it's only one additional level of passing props. It seems that depending on the scope of the app, you might want to pass props up to 1-2 levels past the redux container and if it's any more than that, then just create another redux container. Then again, if it's an even more complex app, then the mixing of sometimes using redux containers and some other times not using them could be even worse for maintainability. In short, my opinion is trying to minimize redux containers wherever possible but definitely not at the expense of complex prop chains, since that's the main point of using redux to begin with.
So it's been over 2 years since I've posted this question, and this whole time
I have been consistently working with React/Redux. My general rule of thumb now
is the following: Use more containers, but try to write components in such a way where they don't need to know about isFetching.
For example, here is a typical example of how I would have built a to-do list before:
function Todos({ isFetching, items }) {
if (isFetching) return <div>Loading...</div>
return (
<ul>
{items.map(item =>
<li key={item.id}>...</li>
)}
</ul>
)
}
Now I would do something more like:
function Todos({ items }) {
if (!items.length) return <div>No items!</div>
return (
<ul>
{items.map(item =>
<li key={item.id}>...</li>
)}
</ul>
)
}
This way, you only have to connect the data, and the component has no concerns about states of asynchronous API calls.
Most things can be written this way. I rarely need isFetching, but when I do it is typically because:
I need to prevent, for example, a submit button from being clicked a second time, which makes an API call, in which case the prop should probably be called disableSubmit rather than isFetching, or
I want to explicitly show a loader when something is waiting for an asynchronous response.
Now, you might think, "wouldn't you want to show a loader when items are being fetched in the above todos example?" but in practice, actually I wouldn't.
The reason for this is that in the above example, let's say you were polling for new todos, or when you add a todo, you "refetch" the todos. What would happen in the first example is that every time this happened, the todos would disappear and get replaced with "Loading..." frequently.
However, in the second example that is not concerned with isFetching, the new items are simply appended/removed. This is much better UX in my opinion.
In fact, before posting this, I went through all the UI code for an exchange interface I wrote which is quite complex and did not find a single instance of having to connect isFetching to a container component that I wrote.
You don't have to dispatch AND load your state in the same place.
In other words, your button can dispatch the async request, while another component can check if you're loading.
So for example:
// < SomeButtonThatFetchesData.js>
const mapDispatchToProps = (dispatch) => ({
onLoad: (payload) =>
dispatch({ type: DATA_LOADED, payload })
});
You'll need to have some middleware to handle a loading state. It needs to update isFetching when you're passing an async payload.
For example:
const promiseMiddleware = store => next => action => {
if (isPromise(action.payload)) {
store.dispatch({ type: ASYNC_START, subtype: action.type });
Then you can use it wherever you want:
// <MyContainer.js>
const mapStateToProps = (state) => ({
isFetching: state.isFetching
});
And load the data in your inner nested component:
// <SomethingThatDependsOnData.js>
const mapStateToProps = (state) => ({
someData: state.someData
});