I am looking at someone else code who updated the state of object in the react lifecyle:componentWillReceiveProps. I am fairly new to react and redux but thought that you do all the updating of state in the reducer useless its local state. Can someone tell me why he is doing it in componentWillReceiveProps? Thanks
componentWillReceiveProps(nextProps) {
if(this.props.isEditingbook && !nextProps.isEditingbook) {
let book = this.props.index.bookDictionary[this.props.currentbook.id]
book.name = this.state.model.name.value
}
this.setState({ ...this.state, ...nextProps})
}
Well, first of all, componentWillrecieveProps has been deprecated because it might cause some problems, take a look here . Instead, React docs point out that you should use componentDidUpdate which is a safe-to-use method.
And answering your question, if you looked a code where that person was using redux, then he used that deprecated method because when you bind a component to redux goblal state (store) through mapStateToProps, it's properties are bind to that component props. So, in other words, whenever the global state changes so does the component props, and if you want to "track" these changes in your component logic, you have to know when it's props are going to change, that's why you use componentWillRecieveProps or componentDidUpdate methods.
Here is how that example code should has been done with componentDidUpdate:
componentDidUpdate(prevProps) { //prevProps is the previous props of the component before being updated
//so, if this.props != prevProps it means that component props have been updated
if(this.props.isEditingbook && !prevProps.isEditingbook) {
let book = this.props.index.bookDictionary[this.props.currentbook.id]
book.name = this.state.model.name.value
}
this.setState({ ...this.state, ...prevProps})
}
Related
i try to compare the prev props and new props and if it is not same update the state.
but i am getting prev props as empty in every time
componentWillReceiveProps = (props, prevProps) => {
if (
props.data.length > 0 &&
props.data !== prevProps.data
) {
this.setState({
data: props.data
});
}
}
when props changed ,I need to compare old and new props , if old and new props are not same need to update the state.
I suggest you to use React Hook. It is powerful library to handle state and props in previous and current value.
https://blog.logrocket.com/how-to-get-previous-props-state-with-react-hooks/
BR
read doc about componentWillReceiveProps. This method provide only 1 argument - nextProps
To answer your original question, componentWillReceiveProps has been deprecated for a while. Ideally you use https://reactjs.org/docs/react-component.html#static-getderivedstatefromprops to achieve what you are doing here. Although this should be used sparingly, I still have a hard time understanding why you would duplicate the state like this.
You could also do componentDidUpdate(prevProps), and then use this.props for the current value.
I haven’t used class based components for a while. I use Hooks now.
I'm facing an issue with Redux and React
I use a redux action to fetch data from an API. When the component mounts, this action is fired and populate the Redux state. I want a second action to be fired with parameters (article) from the redux state.
My issue is that when I fire the second action, the redux state is still empty, so article is null, which causes an error.
componentDidMount() {
const { targetArticle, userVisit, match, article } = this.props
targetArticle(match.params.slug);
userVisit(match.params.slug, article.title);
}
I've already checked other topics on the subject like this one, but none of them works for me. How can I achieve that?
Thanks
You'd probably have to use componentDidUpdate lifecycle method. So given that userVisit is dependent on the result of targetArticle and assuming you are looking to this.props. for the updated Redux state, something like this should get you there:
componentDidUpdate(prevProps) {
if(prevProps.article !== this.props.article) {
// Now you have access to targetArticle's result and updated Redux state
userVisit(match.params.slug, this.props.article.title)
}
}
More in the docs: https://reactjs.org/docs/react-component.html#componentdidupdate
So I've rewrote my code a bit to use state instead of modifying props since it is not what I should do. The problem that occurred now is that when componentDidMount runs props are still not fetched from the backend, therefore the if statements in the function are always false.
componentDidMount() {
this.props.getTypes('sport');
this.props.getSchema();
this.props.getDomainForm();
if(Object.keys(this.props.schema).length) {
this.setState({schema: this.props.schema})
}
if(Object.keys(this.props.formData).length) {
this.setState({form: this.props.formData})
}
}
const mapStateToProps = (state) => {
return {
schema: state.admin.settings.Domains.schema.data || {},
formData: state.admin.settings.Domains.domain.data || {},
types: state.admin.settings.Domains.types.data || {},
}
};
I've stepped trough the code and it seems like componentDidMount runs only once. Since componentWillRecieveProps is deprecated I am unsure what to do to fix this, and I hope you guys can help me with this one.
PS. there is no problems with fetch actions and reducers works perfectly I haven't changed anything there and redux debugger is displaying the results correctly.
i think the problem is your fetch is async and it takes little bit time to accomplish the task, and before the fetch is been finished , your component mounts on the DOM.
as you noted you can see the data is been received via redux debugger and you have no problem with it , so i'm guessing that you passed the initial state as empty object or array to your state. so then your component receives data through props and you are not updating the state to reRender the component , what you need to do is just use componentWillReceiveProps to update the state whenever the new data is been received by just checking if current props is not equal to previous props , some code like this :
componentWillReceiveProps = (nextProps) => {
if(this.props.yourPropsFromRedux != nextProps.yourPropsFromRedux ) {
this.setState({ yourState: nextProps.yourPropsFromRedux })
}
}
As a replacement of componentWillReceiveProps there was introduced static getDerivedStateFromProps(props, state) method, it's called each time component receives new props, so it might be helpful for you. Here's the docs.
Using componentDidUpdate along with componentDidMount is more suitable for this situation. componentDidMount will set the state for initial render and componentDidUpdate will set state for future renders. Don't forget to test the prevProps parameter of the componentDidUpdate method with current props to check if the data has changed or not. Read the documentation here
I recently wanted to upgrade my knowledge of React, so I started from the component lifecycle methods. The first thing that got me curious, is this componentWillReceiveProps. So, the docs are saying that it's fired when component is receiving new (not necessarily updated) props. Inside that method we can compare them and save into the state if needed.
My question is: Why do we need that method, if changes in props of that component (inside parent render) will trigger the re-render of this child component?
One common use case are state (this.state) updates that may be necessary in response to the updated props.
Since you should not try to update the component's state via this.setState() in the render function, this needs to happen in componentWillReceiveProps.
Additionally, if some prop is used as a parameter to some fetch function you should watch this prop in componentWillReceiveProps to re-fetch data using the new parameter.
Usually componentDidMount is used as a place where you trigger a method to fetch some data. But if your container, for example, UserData is not unmounted and you change userId prop, the container needs to fetch data of a user for corresponding userId.
class UserData extends Component {
componentDidMount() {
this.props.getUser(this.props.userId);
}
componentWillReceiveProps(nextProps) {
if (this.props.userId !== nextProps.userid) {
this.props.getUser(nextProps.userId);
}
}
render() {
if (this.props.loading) {
return <div>Loading...</div>
}
return <div>{this.user.firstName}</div>
}
}
It is not a full working example. Let's imagine that getUser dispatch Redux action and Redux assign to the component user, loading and getUser props.
It 'serves' as an opportunity to react to the incoming props to set the state of your application before render. If your call setState after render you will re-render infinitely and that's why you're not allowed to do that, so you can use componentWillReceiveProps instead.
But... you are beyond CORRECT in your confusion, so correct in fact that they are deprecating it and other Will-lifecycle hooks Discussion Deprecation.
There are other ways to accomplish what you want to do without most of those Will-lifecycle methods, one way being don't call setState after render, just use the new incoming props directly in render (or wherever) to create the stateful value you need and then just use the new value directly, you can then later set state to keep a reference for the next iteration ex: this.state.someState = someValue, this will accomplish everything and not re-render the component in an infinite loop.
Use this as an opportunity to react to a prop transition before render() is called by updating the state using this.setState(). The old props can be accessed via this.props. Calling this.setState() within this function will not trigger an additional render.
Look at this article
the componentWillReceiveProps will always receive as param "NxtProps", componentWillReceiveProps is called after render().
some people use this method use this to compare nxtProps and this.props to check, if something should happen before the component call render, and to some validations.
check the react's documentation to know more about react lifecycle!
hope this could help you!
changes in props of that component (inside parent render) will trigger the re-render of this child component
You are absolutely right. You only need to use this method if you need to react to those changes. For instance, you might have a piece of state in a child component that is calculated using multiple props.
Small Example:
class Test extends Component {
state = {
modified: "blank"
};
componentDidMount(){
this.setState({
modified: `${this.props.myProp} isModified`
});
}
componentWillReceiveProps(nextProps) {
this.setState({
modified: `${nextProps.myProp} isModified`
});
}
render() {
return <div className="displayed">{this.state.modified}</div>
}
}
In this example, componentDidMount sets the state using this.props. When this component receives new props, without componentWillReceiveProps, this.state.modified would never be updated again.
Of course, you could just do {this.props.myProp + "IsModified"} in the render method, but componentWillReceiveProps is useful when you need to update this.state on prop changes.
I'm probably missing something very obvious and would like to clear myself.
Here's my understanding.
In a naive react component, we have states & props. Updating state with setState re-renders the entire component. props are mostly read only and updating them doesn't make sense.
In a react component that subscribes to a redux store, via something like store.subscribe(render), it obviously re-renders for every time store is updated.
react-redux has a helper connect() that injects part of the state tree (that is of interest to the component) and actionCreators as props to the component, usually via something like
const TodoListComponent = connect(
mapStateToProps,
mapDispatchToProps
)(TodoList)
But with the understanding that a setState is essential for the TodoListComponent to react to redux state tree change(re-render), I can't find any state or setState related code in the TodoList component file. It reads something like this:
const TodoList = ({ todos, onTodoClick }) => (
<ul>
{todos.map(todo =>
<Todo
key={todo.id}
{...todo}
onClick={() => onTodoClick(todo.id)}
/>
)}
</ul>
)
Can someone point me in the right direction as to what I am missing?
P.S I'm following the todo list example bundled with the redux package.
The connect function generates a wrapper component that subscribes to the store. When an action is dispatched, the wrapper component's callback is notified. It then runs your mapState function, and shallow-compares the result object from this time vs the result object from last time (so if you were to rewrite a redux store field with its same value, it would not trigger a re-render). If the results are different, then it passes the results to your "real" component" as props.
Dan Abramov wrote a great simplified version of connect at (connect.js) that illustrates the basic idea, although it doesn't show any of the optimization work. I also have links to a number of articles on Redux performance that discuss some related ideas.
update
React-Redux v6.0.0 made some major internal changes to how connected components receive their data from the store.
As part of that, I wrote a post that explains how the connect API and its internals work, and how they've changed over time:
Idiomatic Redux: The History and Implementation of React-Redux
My answer is a little out of left field. It sheds light on a problem that led me to this post. In my case it seemed the app was Not re-rendering, even though it received new props.
React devs had an answer to this often asked question something to the tune that if the (store) was mutated, 99% of the time that's the reason react won't re-render.
Yet nothing about the other 1%. Mutation was not the case here.
TLDR;
componentWillReceiveProps is how the state can be kept synced with the new props.
Edge Case: Once state updates, then the app does re-render !
It turn out that if your app is using only state to display its elements, props can update, but state won't, so no re-render.
I had state that was dependent on props received from redux store. The data I needed wasn't in the store yet, so I fetched it from componentDidMount, as is proper. I got the props back, when my reducer updated store, because my component is connected via mapStateToProps. But the page didn't render, and state was still full of empty strings.
An example of this is say a user loaded an "edit post" page from a saved url. You have access to the postId from the url, but the info isn't in store yet, so you fetch it. The items on your page are controlled components - so all the data you're displaying is in state.
Using redux, the data was fetched, store was updated, and the component is connected, but the app didn't reflect the changes. On closer look, props were received, but app didn't update. state didn't update.
Well, props will update and propagate, but state won't.
You need to specifically tell state to update.
You can't do this in render(), and componentDidMount already finished it's cycles.
componentWillReceiveProps is where you update state properties that depend on a changed prop value.
Example Usage:
componentWillReceiveProps(nextProps){
if (this.props.post.category !== nextProps.post.category){
this.setState({
title: nextProps.post.title,
body: nextProps.post.body,
category: nextProps.post.category,
})
}
}
I must give a shout out to this article that enlightened me on the solution that dozens of other posts, blogs, and repos failed to mention. Anyone else who has had trouble finding an answer to this evidently obscure problem, Here it is:
ReactJs component lifecycle methods — A deep dive
componentWillReceiveProps is where you'll update state to keep in sync with props updates.
Once state updates, then fields depending on state do re-render !
This answer is a summary of Brian Vaughn's article entitled You Probably Don't Need Derived State (June 07, 2018).
Deriving state from props is an anti-pattern in all its forms. Including using the older componentWillReceiveProps and the newer getDerivedStateFromProps.
Instead of deriving state from props, consider the following solutions.
Two best practice recommendations
Recommendation 1. Fully controlled component
function EmailInput(props) {
return <input onChange={props.onChange} value={props.email} />;
}
Recommendation 2. Fully uncontrolled component with a key
// parent class
class EmailInput extends Component {
state = { email: this.props.defaultEmail };
handleChange = event => {
this.setState({ email: event.target.value });
};
render() {
return <input onChange={this.handleChange} value={this.state.email} />;
}
}
// child instance
<EmailInput
defaultEmail={this.props.user.email}
key={this.props.user.id}
/>
Two alternatives if, for whatever reason, the recommendations don't work for your situation.
Alternative 1: Reset uncontrolled component with an ID prop
class EmailInput extends Component {
state = {
email: this.props.defaultEmail,
prevPropsUserID: this.props.userID
};
static getDerivedStateFromProps(props, state) {
// Any time the current user changes,
// Reset any parts of state that are tied to that user.
// In this simple example, that's just the email.
if (props.userID !== state.prevPropsUserID) {
return {
prevPropsUserID: props.userID,
email: props.defaultEmail
};
}
return null;
}
// ...
}
Alternative 2: Reset uncontrolled component with an instance method
class EmailInput extends Component {
state = {
email: this.props.defaultEmail
};
resetEmailForNewUser(newEmail) {
this.setState({ email: newEmail });
}
// ...
}
As I know only thing redux does, on change of store's state is calling componentWillRecieveProps if your component was dependent on mutated state and then you should force your component to update
it is like this
1-store State change-2-call(componentWillRecieveProps(()=>{3-component state change}))