In parent component App I render child component PersonsTable:
var App = React.createClass({
addPerson: function() {
// building personToAdd object and passing to personsTable...
this.refs.personsTable.setState({personToAdd: person});
},
render: function() {
return (
<div>
<PersonsTable ref="personsTable" />
...
</div>
);
},
});
Now I'm passing a new object by calling setState method of PersonsTable.
If I call setProps method, it returns a warning
Uncaught Invariant Violation: setProps(...): You called setProps on a component with a parent. This is an anti-pattern since props will get reactively updated when rendered. Instead, change the owner's render method to pass the correct value as props to the component where it is created.
How do I correctly pass such an object to PersonsTable without using setState method?
Here is full code https://jsfiddle.net/jpt5uy1k/
It looks like you're trying to implement an anti-pattern by calling setState on a ref. It's better to pass props to the child and use those. If you need state, set it in a parent and pass it down as a prop.
<div>
<PersonsTable aProp={someCoolInfoOrParentState} />
...
</div>
Refs should be used only when you need to "reach out" and get hold of an actual DOM node for one reason or another. Also, you generally want state in as few places as possible, since it can be complicated and requires extra "machinery" to make work. Better to keep state in a single place and thread it down through other components.
See this from https://github.com/reactjs/react-basic:
We tend to prefer our data model to be immutable. We thread functions through that can update state as a single atom at the top.
Related
Does React re-render all components and sub components every time setState() is called?
If so, why? I thought the idea was that React only rendered as little as needed - when state changed.
In the following simple example, both classes render again when the text is clicked, despite the fact that the state doesn't change on subsequent clicks, as the onClick handler always sets the state to the same value:
this.setState({'test':'me'});
I would've expected that renders would only happen if state data had changed.
Here's the code of the example, as a JS Fiddle, and embedded snippet:
var TimeInChild = React.createClass({
render: function() {
var t = new Date().getTime();
return (
<p>Time in child:{t}</p>
);
}
});
var Main = React.createClass({
onTest: function() {
this.setState({'test':'me'});
},
render: function() {
var currentTime = new Date().getTime();
return (
<div onClick={this.onTest}>
<p>Time in main:{currentTime}</p>
<p>Click me to update time</p>
<TimeInChild/>
</div>
);
}
});
ReactDOM.render(<Main/>, document.body);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react-dom.min.js"></script>
Does React re-render all components and sub-components every time setState is called?
By default - yes.
There is a method boolean shouldComponentUpdate(object nextProps, object nextState), each component has this method and it's responsible to determine "should component update (run render function)?" every time you change state or pass new props from parent component.
You can write your own implementation of shouldComponentUpdate method for your component, but default implementation always returns true - meaning always re-run render function.
Quote from official docs http://facebook.github.io/react/docs/component-specs.html#updating-shouldcomponentupdate
By default, shouldComponentUpdate always returns true to prevent
subtle bugs when the state is mutated in place, but if you are careful to
always treat the state as immutable and to read-only from props and state
in render() then you can override shouldComponentUpdate with an
implementation that compares the old props and state to their
replacements.
Next part of your question:
If so, why? I thought the idea was that React only rendered as little as needed - when the state changed.
There are two steps of what we may call "render":
Virtual DOM renders: when render method is called it returns a new virtual dom structure of the component. As I mentioned before, this render method is called always when you call setState(), because shouldComponentUpdate always returns true by default. So, by default, there is no optimization here in React.
Native DOM renders: React changes real DOM nodes in your browser only if they were changed in the Virtual DOM and as little as needed - this is that great React's feature which optimizes real DOM mutation and makes React fast.
No, React doesn't render everything when the state changes.
Whenever a component is dirty (its state changed), that component and its children are re-rendered. This, to some extent, is to re-render as little as possible. The only time when render isn't called is when some branch is moved to another root, where theoretically we don't need to re-render anything. In your example, TimeInChild is a child component of Main, so it also gets re-rendered when the state of Main changes.
React doesn't compare state data. When setState is called, it marks the component as dirty (which means it needs to be re-rendered). The important thing to note is that although render method of the component is called, the real DOM is only updated if the output is different from the current DOM tree (a.k.a diffing between the Virtual DOM tree and document's DOM tree). In your example, even though the state data hasn't changed, the time of last change did, making Virtual DOM different from the document's DOM, hence why the HTML is updated.
Yes. It calls the render() method every time we call setState only except when shouldComponentUpdate returns false.
Even though it's stated in many of the other answers here, the component should either:
implement shouldComponentUpdate to render only when state or properties change
switch to extending a PureComponent, which already implements a shouldComponentUpdate method internally for shallow comparisons.
Here's an example that uses shouldComponentUpdate, which works only for this simple use case and demonstration purposes. When this is used, the component no longer re-renders itself on each click, and is rendered when first displayed, and after it's been clicked once.
var TimeInChild = React.createClass({
render: function() {
var t = new Date().getTime();
return (
<p>Time in child:{t}</p>
);
}
});
var Main = React.createClass({
onTest: function() {
this.setState({'test':'me'});
},
shouldComponentUpdate: function(nextProps, nextState) {
if (this.state == null)
return true;
if (this.state.test == nextState.test)
return false;
return true;
},
render: function() {
var currentTime = new Date().getTime();
return (
<div onClick={this.onTest}>
<p>Time in main:{currentTime}</p>
<p>Click me to update time</p>
<TimeInChild/>
</div>
);
}
});
ReactDOM.render(<Main/>, document.body);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react-dom.min.js"></script>
It seems that the accepted answers are no longer the case when using React hooks (with primitive values, see comments on this answer for details). You can see in this code sandbox that the class component is rerendered when the state is set to the same value, while in the function component, setting the state to the same value doesn't cause a rerender.
https://codesandbox.io/s/still-wave-wouk2?file=/src/App.js
React 18 and beyond
Starting from React 18 all state updates are automatically batched. In this way, React groups multiple state updates into a single re-render for better performance.
So when you update your state, React always try to batch these updates in a group update, causing fewer render than setState calls. The behaviour is the same when using hooks.
You can read the very long explanation in the Automatic batching for React 18 announcement.
React 17 and below
In React 17 and below, only updates inside React event handlers are batched. Updates triggered from promises, setTimeout, native event handlers, or other events are not batched in React by default.
Another reason for "lost update" can be the next:
If the static getDerivedStateFromProps is defined then it is rerun in every update process according to official documentation https://reactjs.org/docs/react-component.html#updating.
so if that state value comes from props at the beginning it is overwrite in every update.
If it is the problem then U can avoid setting the state during update, you should check the state parameter value like this
static getDerivedStateFromProps(props: TimeCorrectionProps, state: TimeCorrectionState): TimeCorrectionState {
return state ? state : {disable: false, timeCorrection: props.timeCorrection};
}
Another solution is add a initialized property to state, and set it up in the first time (if the state is initialized to non null value.)
Not All Components.
the state in component looks like the source of the waterfall of state of the whole APP.
So the change happens from where the setState called. The tree of renders then get called from there. If you've used pure component, the render will be skipped.
Regardless of the well explained answers here, there may be other reasons why you don't see the change you expect post changing the props or state:
Watch out for any event.preventDefault(); in the code where you want to re-render by a state \ props change, as it will cancel any cancelable event following this statement.
You could use setState() only after comparing the current state value and the new one and they are different.
function App() {
const [currentPanel, setCurrentPanel] = useState(ProfilePanel); // ProfilePanel is a component
return (
<div className={styles.App}>
{currentPanel}
</div>
);
}
In code i set the component "ProfilePanel" to a "curentPanlel" state, then in App i change the component in state, and this render an another panel. the problem is that i dont know how to pass props when i render it like this.
i tried the {currentPanel()} but is return an error.
please help to find a method to solve this, or if this method to render a component in state are absolutly wrong tell how to do this another way.
the problem is that i dont know how to pass props when i render it like this
You'd do it by using an initial capital letter for the state member (CurrentPanel instead of currentPanel), and then using it as normal (<CurrentPanel someProp="some value" />). (It has to be initially-capped because that's how JSX knows it's supposed to be a component, not a tag name.) But, you'll struggle to set a different component function in state, because component functions are, well, functions, and when you pass a function to a state setter, it thinks you're using the callback version of the state setter and calls your function, rather than setting it in state.
If you absolutely have to hold a component function in state, wrap it in an object, but it's much more likely that there's a better solution to the overall problem you're trying to solve.
Does React re-render all components and sub components every time setState() is called?
If so, why? I thought the idea was that React only rendered as little as needed - when state changed.
In the following simple example, both classes render again when the text is clicked, despite the fact that the state doesn't change on subsequent clicks, as the onClick handler always sets the state to the same value:
this.setState({'test':'me'});
I would've expected that renders would only happen if state data had changed.
Here's the code of the example, as a JS Fiddle, and embedded snippet:
var TimeInChild = React.createClass({
render: function() {
var t = new Date().getTime();
return (
<p>Time in child:{t}</p>
);
}
});
var Main = React.createClass({
onTest: function() {
this.setState({'test':'me'});
},
render: function() {
var currentTime = new Date().getTime();
return (
<div onClick={this.onTest}>
<p>Time in main:{currentTime}</p>
<p>Click me to update time</p>
<TimeInChild/>
</div>
);
}
});
ReactDOM.render(<Main/>, document.body);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react-dom.min.js"></script>
Does React re-render all components and sub-components every time setState is called?
By default - yes.
There is a method boolean shouldComponentUpdate(object nextProps, object nextState), each component has this method and it's responsible to determine "should component update (run render function)?" every time you change state or pass new props from parent component.
You can write your own implementation of shouldComponentUpdate method for your component, but default implementation always returns true - meaning always re-run render function.
Quote from official docs http://facebook.github.io/react/docs/component-specs.html#updating-shouldcomponentupdate
By default, shouldComponentUpdate always returns true to prevent
subtle bugs when the state is mutated in place, but if you are careful to
always treat the state as immutable and to read-only from props and state
in render() then you can override shouldComponentUpdate with an
implementation that compares the old props and state to their
replacements.
Next part of your question:
If so, why? I thought the idea was that React only rendered as little as needed - when the state changed.
There are two steps of what we may call "render":
Virtual DOM renders: when render method is called it returns a new virtual dom structure of the component. As I mentioned before, this render method is called always when you call setState(), because shouldComponentUpdate always returns true by default. So, by default, there is no optimization here in React.
Native DOM renders: React changes real DOM nodes in your browser only if they were changed in the Virtual DOM and as little as needed - this is that great React's feature which optimizes real DOM mutation and makes React fast.
No, React doesn't render everything when the state changes.
Whenever a component is dirty (its state changed), that component and its children are re-rendered. This, to some extent, is to re-render as little as possible. The only time when render isn't called is when some branch is moved to another root, where theoretically we don't need to re-render anything. In your example, TimeInChild is a child component of Main, so it also gets re-rendered when the state of Main changes.
React doesn't compare state data. When setState is called, it marks the component as dirty (which means it needs to be re-rendered). The important thing to note is that although render method of the component is called, the real DOM is only updated if the output is different from the current DOM tree (a.k.a diffing between the Virtual DOM tree and document's DOM tree). In your example, even though the state data hasn't changed, the time of last change did, making Virtual DOM different from the document's DOM, hence why the HTML is updated.
Yes. It calls the render() method every time we call setState only except when shouldComponentUpdate returns false.
Even though it's stated in many of the other answers here, the component should either:
implement shouldComponentUpdate to render only when state or properties change
switch to extending a PureComponent, which already implements a shouldComponentUpdate method internally for shallow comparisons.
Here's an example that uses shouldComponentUpdate, which works only for this simple use case and demonstration purposes. When this is used, the component no longer re-renders itself on each click, and is rendered when first displayed, and after it's been clicked once.
var TimeInChild = React.createClass({
render: function() {
var t = new Date().getTime();
return (
<p>Time in child:{t}</p>
);
}
});
var Main = React.createClass({
onTest: function() {
this.setState({'test':'me'});
},
shouldComponentUpdate: function(nextProps, nextState) {
if (this.state == null)
return true;
if (this.state.test == nextState.test)
return false;
return true;
},
render: function() {
var currentTime = new Date().getTime();
return (
<div onClick={this.onTest}>
<p>Time in main:{currentTime}</p>
<p>Click me to update time</p>
<TimeInChild/>
</div>
);
}
});
ReactDOM.render(<Main/>, document.body);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.0.0/react-dom.min.js"></script>
It seems that the accepted answers are no longer the case when using React hooks (with primitive values, see comments on this answer for details). You can see in this code sandbox that the class component is rerendered when the state is set to the same value, while in the function component, setting the state to the same value doesn't cause a rerender.
https://codesandbox.io/s/still-wave-wouk2?file=/src/App.js
React 18 and beyond
Starting from React 18 all state updates are automatically batched. In this way, React groups multiple state updates into a single re-render for better performance.
So when you update your state, React always try to batch these updates in a group update, causing fewer render than setState calls. The behaviour is the same when using hooks.
You can read the very long explanation in the Automatic batching for React 18 announcement.
React 17 and below
In React 17 and below, only updates inside React event handlers are batched. Updates triggered from promises, setTimeout, native event handlers, or other events are not batched in React by default.
Another reason for "lost update" can be the next:
If the static getDerivedStateFromProps is defined then it is rerun in every update process according to official documentation https://reactjs.org/docs/react-component.html#updating.
so if that state value comes from props at the beginning it is overwrite in every update.
If it is the problem then U can avoid setting the state during update, you should check the state parameter value like this
static getDerivedStateFromProps(props: TimeCorrectionProps, state: TimeCorrectionState): TimeCorrectionState {
return state ? state : {disable: false, timeCorrection: props.timeCorrection};
}
Another solution is add a initialized property to state, and set it up in the first time (if the state is initialized to non null value.)
Not All Components.
the state in component looks like the source of the waterfall of state of the whole APP.
So the change happens from where the setState called. The tree of renders then get called from there. If you've used pure component, the render will be skipped.
Regardless of the well explained answers here, there may be other reasons why you don't see the change you expect post changing the props or state:
Watch out for any event.preventDefault(); in the code where you want to re-render by a state \ props change, as it will cancel any cancelable event following this statement.
You could use setState() only after comparing the current state value and the new one and they are different.
I'm trying to pass a ref of a component to another component. Since string refs are being deprecated I'm using callback refs.
So I have something similar to this:
<One ref={c => this.one = c}/>
<Two one={this.one}/>
The problem is that whenever I try to access this.props.one inside Two I get undefined.
I have even tried this on Two:
componentDidMount(){
setTimeout(()=>{
console.log(this.props.one);
},5000)
}
It seems the problem is that when the prop is created, the ref doesn't exist yet since it's created once One is mounted. But I don't know how to "refresh" the props on Two to get the ref to the mounted component.
So what's the proper way of passing a ref to another component?
Edit
Some users have suggested to encapsulate that logic in a higher component, which in itself renders those other child components.
The problem with that approach is that you can't create reusable logic and you have to repeat the same logic over and over in those encapsulating components.
Let's say you want to create a generic <Form> component which encapsulates the submit logic to your store, error checking, etc. And you do something like this:
<Form>
<Input/>
<Input/>
<Input/>
<Input/>
<SubmitButton/>
</Form>
In this example <Form> can't access the instances (and methods) of the children since this.props.children doesn't return those instances. It returns some list of pseudo components.
So how can you check if a certain <Input/> has detected a validation error without passing a ref?
You have to encapsulate those components in another component with the validation logic. For example in <UserForm>. But since each form is different the same logic has to be copied in <CategoryForm>, <GoupForm>, etc. This is terribly inefficient which is why I want to encapsulate the validation logic in <Form> and pass references of the <Input> components to <Form>.
In general the "ref" feature is an anti-pattern in React. It exists to enable side-effect driven development, however in order to benefit the most from the React way of programming you should try to avoid "refs" if possible.
As for your particular issue, passing a child a ref to it's sibling is a chicken vs. egg scenario. The ref callback is fired when the child is mounted, not during render which is why your example doesn't work. One thing you can try is pushing the ref into state and then reading from state into the other child. So:
<One ref={c => !this.state.one && this.setState({ one: c })}/>
<Two one={this.state.one}/>
Note: without the !this.state.one this will cause an infinite loop.
Here is a codepen example of this working (look at the console to see the sibling ref logged): http://codepen.io/anon/pen/pbqvRA
This is now much simpler using the new ref api (available since React 16 - thanks to perilandmishap for pointing that out).
class MyComponent extends React.Component {
constructor (props) {
super(props);
this.oneRef = React.createRef();
}
render () {
return (
<React.Fragment>
<One ref={this.oneRef} />
<Two one={this.oneRef} />
</React.Fragment>
}
}
}
You would consume the prop in Two like:
this.props.one.current
A few things of note with this approach:
The ref will be an object with a current property. That property will be null until the element/component is mounted. Once it's mounted, it will be the instance of One. It should be safe to reference it once <Two /> is mounted.
Once the <One /> instance is unmounted, the current property on the ref returns to being null.
In general, if you need to pass a reference to something that may not be set at call time, you can pass a lambda instead:
<One ref={c => this.one = c}/>
<Two one={() => this.one}/>
and then reference it as
this.props.one()
If it has been set when you call it, you'll get a value. Before that, you'll get undefined (assuming it hasn't otherwise been initialized).
It bears noting that you won't necessarily re-render when it becomes available, and I would expect it to be undefined on the first render. This is something that using state to hold your reference does handle, but you won't get more than one re-render.
Given all that, I would recommend moving whatever code was using the ref to One in Two up into the component that is rendering One and Two, to avoid all the issues with both this strategy, and the one in #Carl Sverre's answer.
I have a situation that I'm sure is common and I just haven't learned the react way for accomplishing it. Let's say I have this:
var appView = new React.createClass({
render: function() {
return (
<div>
<SomeSubview/>
</div>
)
}
});
React.render(
React.createElement(appView),
$('#app').get(0)
);
My question is how should I create the SomeSubView react component so that it can render properly without any data, and then later render showing some data when the data is available. I have pub/sub system set up, so I'd like to be able to subscribe to an event and get the data to SomeSubView that way. SomeSubView might look something like this:
SomeSubView = new React.createClass({
componentDidMount: function() {
pubsub.subscribe({
callback: function() {
// something the sets the state or a prop of this component
}
});
},
render: function() {
// something that renders properly when
// there is no data and renders the data when there is data
return (
<div></div>
)
}
});
I can't tell if this a case for state or props on the react component? I don't know if it's best practice to put conditionals in the render function?
In your SomeSubView just check if data is available in your render function, but before returning the markup.
Like this:
SomeSubView = new React.createClass({
componentDidMount: function() {
pubsub.subscribe({
callback: function() {
// something the sets the state or a prop of this component
}
});
},
render: function() {
// something that renders properly when
if( this.state.data.length > 0 ){
var data = <li>{this.state.data}</li>;
}
return (
<div>{data}</div>
)
}
});
If the variable data is not set, React will simply pass over it as non-existent.
You can of course also use .map() on your state data to loop out markup just like in most render examples.
You have to use state like user3728205 said, especifically setState().
setState(function|object nextState[, function callback])
Merges nextState with the current state. This is the primary method
you use to trigger UI updates from event handlers and server request
callbacks.
The first argument can be an object (containing zero or more keys to
update) or a function (of state and props) that returns an object
containing keys to update.
Here is the simple object usage...
setState({mykey: 'my new value'});
What this says is that "whenever" you update your state via setState, React will execute the method render again for you. So, you should put yor display logic based on the state, when it changes the view displayed will change too.
I say "whenever" because React doesn't fire re-render immediatily, but creates a pending state transition.
NEVER mutate this.state directly, as calling setState() afterwards may
replace the mutation you made. Treat this.state as if it were
immutable.
setState() does not immediately mutate this.state but creates a
pending state transition. Accessing this.state after calling this
method can potentially return the existing value.
There is no guarantee of synchronous operation of calls to setState
and calls may be batched for performance gains.
setState() will always trigger a re-render unless conditional
rendering logic is implemented in shouldComponentUpdate(). If mutable
objects are being used and the logic cannot be implemented in
shouldComponentUpdate(), calling setState() only when the new state
differs from the previous state will avoid unnecessary re-renders.
For more information about the magic of React you should read this.
https://facebook.github.io/react/docs/reconciliation.html
A simple example that maybe can help.
And i recommend read the flux architecture that is very easy to understand and implement (is about utilizing a unidirectional data flow), and you have implementations like Fluxxor that facilitates the use of flux. This is for your pubsub part.