I don't feel right to store a function in a reactjs state, but not sure any disadvantage? Could anyone help analyze it?
view1: function() {
return <div>view1</view>
}
view2: fucntion() {
return <div>view2</view>
}
goView1: function() {
this.setState({contentView: view1})
}
goView2: function() {
this.setState({contentView: view2})
}
render: function () {
return(
{this.state.contentView()}
)
}
There're a few common gotchas about state in react:
Don't mutate state directly, use setState instead
Don't use state when not referenced in render, use instance variable instead.
Well, it seems fine to use state as function, since it's used in your render function to return what to render? Alright, it might not be an anti-pattern, but a better place to put those functions might be in your props, aka render prop, a few reasons:
Think state as your component's data model.
Data are not stale, it changes over time, it could be results from async operations, ui states after user interactions, controlled forms values etc.
Just like redux stores your app's global state, react state should store your component's local state that changes over time, while functions most of time, does nothing more than deferring execution.
Render props is different, it offers IoC (Inversion of Control) for free.
Props most of time similar to local state, should be concerned with UI rendering. However, unlike state owned/managed by component itself, props are passed from parents/clients of the component.
Event handlers for example, event target (usually DOM elements like button, input etc) doesn't need to know how to handle events when creating the component, instead it yields control back to component client/consumer who might need to use setState in its handleEventName handler to update certain container's state shared across children.
Some library (e.g., react router4) also shifted from HOC to render props (e.g., react 16.3 new context API - provider/consumer pair) in favor of its flexibility and explicitness. Instead of composing HOCs before runtime for static version of final enhanced component, you can declare what to render using render props and composing them at runtime in render functions. Thus, you get a clear separation between data (state/props) provider and consumer (where render props are passed from).
Regarding any performance (re-render) concerns, i think it's totally fine to use state as function, since most performance tricks are done by using shouldComponentUpdate hook with shallow compare state/props references (e.g. React.PureComponent, Redux Connect etc), so it's where immutability and memoization comes into play.
Related
Sometimes, we only need to use the accessor/mutator of a shared state (e.g: setBlockPickerMenu).
const [blockPickerMenu, setBlockPickerMenu] = useRecoilState(blockPickerMenuState);
...
setBlockPickerMenu(null)
And we don't need the value itself (e.g: blockPickerMenu).
What happens inside React when we're doing the above? Does the component subscribes to changes to blockPickerMenu even though we don't actively use it? Does it perform needless re-renders upon changes? Is there a way to optimize things somehow?
The above example uses Recoil, but I assumed it'd work similarly for any shared state (Redux, etc.)
useRecoilState calls useRecoilValue which will implicitly subscribe the component to the given state.
function useRecoilState(recoilState) {
// ...
return [useRecoilValue(recoilState), useSetRecoilState(recoilState)];
}
So yes, it subscribed even if the state isn't used when only needing the setter.
If you want to only be subscribed to the setter, call useSetRecoilState(state).
I assumed it'd work similarly for any shared state (Redux, etc.)
You can't assume, every library and its implementation, for example in Redux, you can't have such a use case since setter and state are decoupled via useDispatch and useSelector.
I'm building an application where I would like to provide separate views for same data.
In my current implementation, data is obtained by web service call and persisted in state of App component in App.js. App component hosts (renders) another component called StackEditor, which acts as a view for this.state.components in App component.
UI elements rendered by StackEditor can be moved around, and to synchronize state of App I do it as below:
<StackEditor
components={this.state.components}
onLocationChanged={this.handleLocationChanged} />
In handleLocationChanged I update the state:
handleLocationChanged(e, data) {
this.setState(prevState => {
// event data copied to state here
return {components: prevState.components};
});
}
As state is now updated, this forces StackEditor to be rendered again, as its property components is bound to state as components={this.state.components} (see in the code snippet above).
This all works, but now I started questioning if I'm doing it right.
Q1: Should I be using state instead of props?
It seems that location of component is mutated in principle, although from StackEditor point of view, it is immutable (I can decide that change is invalid and not to update the state in event listener).
Q2: Is it possible to share part of the state between 2 components in React?
If I somehow convert StackEditor from getting components from state instead of props, will I get notification on state changed by child component (StackEditor) in my parent component (App)?
Q3: Also, are props more convenient to use than state in general?
When I created another component following HOC guidelines (https://reactjs.org/docs/higher-order-components.html) I discovered that props are easily forwarded to "wrapped" component, but not state. If I provide a function to call back via property (as I did above), "wrapped" component can easily call it, without even noticing that it's "wrapped". I don't see how I can easily notify "wrapped" component about state change in "wrapper", without writing some extra code.
If you imagine your application to be a tree of components in a well designed app it's usually like this:
the leafs are stateless components . They decide how data is rendered.
the nodes are stateful components. They decide which components and data to render.
Q1: Should I be using state instead of props?
It depends on which category of components you have (node or leaf).
Q2: Is it possible to share part of the state between 2 components in
React?
If you feel that your app has a lot of state that mutates and needs to be used by several components spread over your tree you usually start to introduce an external state management library (e.g. redux). Components can subscribe to your store and become stateless as your store now handles the state.
Q3: Also, are props more convenient to use than state in general?
They solve different problems so you can't really say that. A stateless component is usually easier to understand but has no capabilities to control anything.
Also read Identify where your state should live and When to use redux.
All that is only a rule of thumb. A lot of the time you will have components that have both state and props because they control parts of your app but delegate other parts to their children.
This all works, but now I started questioning if I'm doing it right.
As far as I can see from the code you provided this looks pretty much as it has to.
I've created a small ReactJS dashboard with the help of SocketIO for live updates. Even though I have the dashboard updating, it bugs me that I'm not quite sure if I did it correctly.
What bugs me the most is the Props in getInitialState as anti-pattern post. I've created a dashboard that gets live updates from a server, requiring no user interaction beyond loading the page. From what I've read, this.state should contain things that will determine whether the component should be re-rendered, and this.props.... I don't know yet.
However, when you initially call React.render(<MyComponent />, ...), you can only pass props. In my case, I get all data from the server, so the initial props just end up in this.state anyway. So all of my components have something like this:
getInitialState: function() {
return {
progress: this.props.progress,
latest_update: this.props.latest_update,
nearest_center: this.props.nearest_center
}
}
Which, unless I've misinterpreted the aforementioned blog post, is an anti-pattern. But I see no other way of injecting the state into the Component, and I don't understand why it's an anti-pattern unless I relabel all of my props to prepend initial on them. If anything, I feel like that's an anti-pattern because now I have to keep track of more variables than I did before (those prepended with initial and those without).
Disclaimer: When I answered this question I was learning / trying to
implement vanilla Flux and I was a bit skeptic about it. Later on I
migrated everything to Redux. So, an advice: Just go with Redux or
MobX. Chances are you won't even need the answer to this question
anymore (except for the science).
Passing the intial state to a component as a prop is an anti-pattern because the getInitialState method is only called the first time the component renders. Meaning that, if you re-render that component passing a different value as a prop, the component will not react accordingly, because the component will keep the state from the first time it was rendered. It's very error prone.
And here is what you should do:
Try to make your components as stateless as possible. Stateless components are easier to test because they render an output based on an input. Simple like that.
But hey.. my components data change.. I can't make them stateless
Yes you can, for most of them. In order to do that, select an outer component to be the state holder. Using your example, you could create a Dashboard component that contains the data, and a Widget component that is completely stateless. The Dashboard is responsible for getting all the data and then rendering multiple Widgets that receive everything they need through props.
But my widgets have some state.. the user can configure them. How do I make them stateless?
Your Widget can expose events that, when handled, cause the state contained in Dashboard to change, causing every Widget to be rerendered. You create "events" in your Widget by having props that receive a function.
Ok, so now, Dashboard keeps the state, but how do I pass the initial state to it?
You have two options. The most recomended one, is that you make an Ajax call in the Dashboard getInitialState method to get the initial state from the server. You can also use Flux, which is a more sophisticated way for managing data. Flux is more of a pattern, rather than an implementation. You can use pure Flux with the Facebook's implementation of the Dispatcher, but you can use third-party implementations like Redux, Alt or Fluxxor.
Alternatively, you can pass this initial state as a prop to the Dashboard, explicitly declaring that this is just the initial state.. like initialData, for instance. If you choose this path, though, you can't pass a different initial state to it aftwards, because it will "remember" the state after the first render.
OBS
You are not quite right in your definitions.
State is used to store mutable data, that is, data that is going to change during the component life-cycle. Changes in the state should be made through the setState method and will cause the component to re-render.
Props are used to pass in imutable data to the components. They should not change during the component life-cycle. Components that only use props are stateless.
This is a relevant source on the "how to pass the initial state to components".
I wonder how
controlled components (e.g an input box) can be implemented, if the data of an app is build upon immutable data and the app uses "===" equality operators in shouldComponentUpdate() for fast re-rendering.
Let's assume deeply nested data and a controlled component somewhere deep in the hierarchy:
When local component state is used (setState()) as one would implement this normally, the changes are not seen by react as the component hierarchy rendering process might skip branches, because the immutable data has not changed. To avoid this, all local component state has to live in the application state, and every event on the controlled component (e.g. typing in an input box) has to result in changing the immutable data.
Although this should work, is this the (only) way controlled components are implemented when immutable data is used??? Doing this all with flux (fire an action, fetch the store data...) might be a lot of overhead/round-trips for something simple as typing into an input box.
A component's state is a great place to put data you don't need to persist or access from multiple places. A common example of this, is an unsubmitted form. When the user does submit the form, you can then pass the local state upwards (callbacks in props) or horizontally (actions, event emitters, apis, etc.).
Also, about not updating, the only time calling setState won't trigger an update in the same component is if you have a overly negative shouldComponentUpdate. If you need local state, the shouldComponentUpdate should take that into account.
There is often a trade-off between placing state to a store or hold it locally. Both approaches work well with immutable collections.
The local state is handled using setState, no direct this.state access. JS strings are immutable, so nothing to care about
onChange: function(event) {
this.setState({value: event.target.value});
}
Sending to a store is almost the same:
onChange: function(event) {
var flux = this.getFlux();
flux.actions.setSomeValue(event.target.value);
}
Store gets the actions and do update/updateIn in immutable collection
If that the flux store is a singleton that maintains the state of the data why do the components use setState and not setProps when accessing the stores? Wouldn't it just mean that I started saving the application state in two (or more) places?
Both the Flux / React documentation and Examples seem to point to setState as the preferred solution, but I've had an interesting conversation with a few colleagues at work and wondered if anyone else came across this
Edit:
You can see what I'm talking about in this url:
https://github.com/facebook/flux/blob/master/examples/flux-chat/js/components/ThreadSection.react.js
Notice how ThreadSection is a child component, that is fetching data directly from a store and using it as a state.
If you follow the React "way" I would have expected the state to be managed by the store - not a child component.
The solution we thought of is to fetch all stores in the top level component (as props) and pass them down to the child components as needed. But that gets rather ugly rather quickly.
We do that because setProps does not work on child components
Understand that you should have 2 kinds of components. Stateful components and view components.
Stateful components can have 3 kinds of states: initial state, user input state, and data store state.
Stateful components are like small entry points in the "widget" that you're assembling. There is no single application-wide entry point anymore for downstream dependency or data injection, because all of these widgets have their own isolated lifecycles. That's why they themselves need to access & listen to stores.
Besides behavorial properties, stateful components do not receive actual data via upstream properties.
Stateful components manage their own state and pass it to their children to render through downstream properties.
Stateful components do not normally render html DOM elements themselves directly. They're more like the controllers in MVC, and use other dumber components, the ones like views in MVC, to actually render DOM elements.
Dumber components are like views so they only contain logic to render DOM elements. Think of them as handlebars.js templates that only receive properties, and simply render those into DOM elements possibly with loops etc. They are stateless renderers.
Hope this answers your question.
According to formal documentation, a store should update the parent component's state, and pass it down via his children props:
When it receives the event from the store, it first requests the new data it needs via the stores' public getter methods. It then calls its own setState() or forceUpdate() methods, causing its render() method and the render() method of all its descendants to run.
We often pass the entire state of the store down the chain of views in a single object, allowing different descendants to use what they need. In addition to keeping the controller-like behavior at the top of the hierarchy, and thus keeping our descendant views as functionally pure as possible, passing down the entire state of the store in a single object also has the effect of reducing the number of props we need to manage.
(facebook flux docs - Overview)
It makes more sense to put store data in the component's state, this is because props may change by a parent component with componentWillReceiveProps. So it makes sense to update the state whenever:
the store's change event is fired and
whenever the props change (putting derivative data related only to the component itself to the state)
Below is a sample component that updates listening to a reflux store and also on props change. I rarely use this.props in the render function, instead I amend them (create derivative data that is only used within the component itself) as new props come in. I constantly run into this pattern so might as well write this down:
var SampleComponent = React.createClass({
mixins: [Reflux.ListenerMixin],
// reusable helper function to build state object
buildStateFromProps: function(props) {
return {
actualHeight: props.height + 20
}
},
// default props if no such was set by a parent component
getDefaultProps: function() {
return {
height: 100
};
},
// initial state with all value set to something default
// even using buildStateFromProps with default props
getInitialState: function() {
// this.props is built before this.state
var state = buildStateFromProps(this.props);
// append default data from store
state.text = '';
},
// happens when the parent component send different
// props data
componentWillReceiveProps: function(nextProps) {
// building derivative data from new props
// reusing buildStateFromProps
this.setState(buildStateFromProps(nextProps));
},
// setting up store to be used by the component
componentDidMount: function() {
// this.listenTo is a helper function ListenerMixin
this.listenTo(sampleStore, sampleUpdated);
},
// is called from the sampleStore update
sampleUpdated: function(sampleData) {
this.setState({
text: sampleData.text
});
},
render: function() {
return (
// ...
// using this.state.text from store updates and
// this.state.height from prop updates
);
}
});
The reason I send props data to state is to avoid cluttering up the render function. Otherwise the render function will contain a lot of code that is not really related to "rendering" the component. Furthermore if this derivative data is used in other parts of the application then it is easy to pull it out from the component and put it into the store.
Hope this helps.
A valid answer to this question sits hidden in the comments to a previous answer:
#idolize you can also pass stores in using React contexts (a hidden,
not yet officially documented feature). It's really nice because you
don't have to do all that passing down the hierarchy. There are a few
articles about contexts, search for it online! – Andy Jul 17 '15 at
18:41