I have two components.
function Parent(props){
const handleClick = () => {
console.log(props.stateA);
};
return <div><Child text={stateB} handleClick={handleClick} /></div>
}
const mapStateToProps = (state) => {
return {
stateA: state.stateA // stateA will be changed somewhere else
stateB: state.stateB
}
};
export default connect(mapStateToProps)(Parent);
function Child(props) {
return <div onClick={props.handleClick}>{props.text}</div>
}
export default React.memo(Child,(prev, next) => {
return prev.text === next.text
});
My problem is when stateA is changed somewhere, clicking on Child will log the previous stateA. I can't access the latest stateA.
You can see, I don't want to Child re-render when stateA changes,it should re-render only when stateB changed. But I want to access the latest stateA in Parent when clicking on Child.
Is there any method to solve this problem?
If the Parent component is a functional component then you can use like this
const [valueA, setValueA] = useState('')
useEffect(() => {
setValueA(props.stateA)
},[props.stateA])
console.log(valueA) // latest Value of stateA
return <div><Child text={stateB} handleClick={handleClick} /></div>
I hope it'll work for you.
You should be able to access props.stateA no problem
const handleClick = () => {
console.log(props.stateA);
};
because you accessing parent's props in handleClick. So if props.stateA is stale then the logical conclusion is the parent doesn't receive the latest props. Can we see how you update props/state?
The problem you are experiencing has nothing to do with Redux.
The Parent component passes 2 props to the child: the text which is changed when needed and handleClick which is changed each render of the Parent component - a new function is created each time.
But the React.memo is checking only the text prop, so the child receives a stale handleClick quite often.
The correct solution is to wrap the handleClick with useCallback and check all props in React.memo (react does this by default).
function Parent(props){
const handleClick = useCallback(() => {
console.log(props.stateA);
}, []);
return <div><Child text={stateB} handleClick={handleClick} /></div>
}
const mapStateToProps = (state) => {
return {
stateA: state.stateA // stateA will be changed somewhere else
stateB: state.stateB
}
};
export default connect(mapStateToProps)(Parent);
function Child(props) {
return <div onClick={props.handleClick}>{props.text}</div>
}
export default React.memo(Child);
You can keep a ref to stateA so it is what is logged when you call handleClick. useRef ensures that the last value is used.
function Parent(props){
const stateARef = useRef(props.stateA);
useEffect(() => {
stateARef.current = props.stateA;
}, [props.stateA])
const handleClick = () => {
console.log(stateARef.current);
};
return <div><Child text={stateB} handleClick={handleClick} /></div>
}
I know that I can wrap HOC with my <Context.Provider> and consume it in all child components.
I would like to consume context in two separate components but they are nested somewhere deeply and closest parent of them is somewhere in the app root. I don't want to provide context to (almost) all components, so I was wondering is it possible to wrap only those two components?
I tried to do it but only first component gets context.
The App structure looks like this:
<App>
<A1>
<A2>
<MyContext.Provider>
<Consumer1/>
</MyContext.Provider>
</A2>
</A1>
<B1>
<B2>
<MyContext.Provider>
<Consumer2/>
</MyContext.Provider>
</B2>
</B1>
</App>
EDIT: I was wrong thinking that wrapping root component will make re-render all child components on context change. Only consumers will rerender so it's perfectly fine to wrap root component.
If you want to have a single value which is shared between multiple parts of the application, then in some form you will need to move that value up to the common ancestor component of the ones that need to consume the value. As you mentioned in the comments, your issue is one of performance and trying not to rerender everything. Having two providers doesn't really help with this, because there will still need to be some component making sure both providers are providing the same value. So that component will end up needing to be a common ancestor of the two providers.
Instead, you can use shouldComponentUpdate (for class components) or React.memo (for functional components) to stop the rerendering process from working its way down the component tree. Deep descendants which are using Context.Consumer will still rerender, and so you can skip over the middle parts of your tree. Here's an example (note the use of React.memo on the intermediate component):
const Context = React.createContext(undefined);
const useCountRenders = (name) => {
const count = React.useRef(0);
React.useEffect(() => {
count.current++;
console.log(name, count.current);
});
}
const App = () => {
const [val, setVal] = React.useState(1);
useCountRenders('App');
React.useEffect(() => {
setTimeout(() => {
console.log('updating app');
setVal(val => val + 1)
}, 1000);
}, [])
return (
<Context.Provider value={val}>
<IntermediateComponent />
</Context.Provider>
);
}
const IntermediateComponent = React.memo((props) => {
useCountRenders('intermediate');
return (
<div>
<Consumer name="first consumer"/>
<UnrelatedComponent/>
<Consumer name="second consumer"/>
</div>
);
})
const Consumer = (props) => {
useCountRenders(props.name);
return (
<Context.Consumer>
{val => {
console.log('running consumer child', props.name);
return <div>consuming {val}</div>
}}
</Context.Consumer>
)
}
const UnrelatedComponent = (props) => {
useCountRenders('unrelated');
return props.children || null;
}
ReactDOM.render(<App />, document.getElementById('root'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.10.2/umd/react.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.10.2/umd/react-dom.development.js"></script>
<div id="root"></div>
When you run the above code, check the logs to see which components rerender. On the first pass, everything renders, but then after a second when the app state changes, only app rerenders. IntermediateComponent, UnrelatedComponent, and even Consumer don't rerender. The function inside the Context.Consumer does rerun, and any thing returned by that function (in this case just a div) will rerender.
As requested by the OP this solution uses mostly hooks but useReducer cannot achieve state sharing under separate providers (as far as I've tried).
It does not require one Provider to be at the root of the app and different reducer can be used for each Provider.
It uses a static state manager but that's an implementation detail, to share the state between several component under different context proviver, one will need something like a shared reference to the state, a way to change it and a way to notify of these changes.
When using the snippet the first button shows the shared state and increment foo when clicked, the second button shows the same shared state and increments bar when clicked:
// The context
const MyContext = React.createContext();
// the shared static state
class ProviderState {
static items = [];
static register(item) {
ProviderState.items.push(item);
}
static unregister(item) {
const idx = ProviderState.items.indexOf(item);
if (idx !== -1) {
ProviderState.items.splice(idx, 1);
}
}
static notify(newState) {
ProviderState.state = newState;
ProviderState.items.forEach(item => item.setState(newState));
}
static state = { foo: 0, bar: 0 };
}
// the state provider which registers to (listens to) the shared state
const Provider = ({ reducer, children }) => {
const [state, setState] = React.useState(ProviderState.state);
React.useEffect(
() => {
const entry = { reducer, setState };
ProviderState.register(entry);
return () => {
ProviderState.unregister(entry);
};
},
[]
);
return (
<MyContext.Provider
value={{
state,
dispatch: action => {
const newState = reducer(ProviderState.state, action);
if (newState !== ProviderState.state) {
ProviderState.notify(newState);
}
}
}}
>
{children}
</MyContext.Provider>
);
}
// several consumers
const Consumer1 = () => {
const { state, dispatch } = React.useContext(MyContext);
// console.log('render1');
return <button onClick={() => dispatch({ type: 'inc_foo' })}>foo {state.foo} bar {state.bar}!</button>;
};
const Consumer2 = () => {
const { state, dispatch } = React.useContext(MyContext);
// console.log('render2');
return <button onClick={() => dispatch({ type: 'inc_bar' })}>bar {state.bar} foo {state.foo}!</button>;
};
const reducer = (state, action) => {
console.log('reducing action:', action);
switch(action.type) {
case 'inc_foo':
return {
...state,
foo: state.foo + 1,
};
case 'inc_bar':
return {
...state,
bar: state.bar + 1,
};
default:
return state;
}
}
// here the providers are used on the same level but any depth would work
class App extends React.Component {
render() {
console.log('render app');
return (
<div>
<Provider reducer={reducer}>
<Consumer1 />
</Provider>
<Provider reducer={reducer}>
<Consumer2 />
</Provider>
<h2>I'm not rerendering my children</h2>
</div>
);
}
}
ReactDOM.render(<App />, document.getElementById('root'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.0/umd/react-dom.production.min.js"></script>
<div id="root"></div>
In the end we have re created something a little like redux with a static state shared by several Provider/Consumer ensembles.
It will work the same no matter where and how deep the providers and consumers are without relying on long nested update chains.
Note that as the OP requested, here there is no need for a provider at the root of the app and therefore the context is not provided to every component, just the subset you choose.
I'm learning react and wanted to try creating a loading component that shows a loading text until a condition is met i.e. the props has the correct information.
The problem is that the element is still loading even if the condition is not met:
Leading Component:
import React from 'react';
const Loading = ({ condition, children }) => (<div>{condition ? children :
'Loading'}</div>);
export default Loading;
Here is my render method for a component that uses the Loading Component:
return
(<Loading condition={props.data && props.data.result && props.data.result.length > 1}>
<div> { ViewHelper.getCatalogItems(props.data) }</div></Loading>);
Now my problem is I'm getting an error when calling { ViewHelper.getCatalogItems(props.data) } becauuse props.data is undefined however I was hoping that the Loading Component wouldn't call the function if the ternary condition in the LoadingComponent was false.
if I change ViewHelper.getData to just some string value, everything seems to work and 'Loading ' is displayed.
Thanks
The fact that Loading component doesn't use children doesn't mean that children aren't rendered. Otherwise there would be nothing to pass as props.children to parent component.
As can be seen in this example, child expression is evaluated despite children prop ignored in parent component.
A proper way to handle this and prevent eager children rendering is to use render prop recipe, which is also known as function as a child:
const Loading = ({ condition, children }) => (
<div>{condition && children ? children() : 'Loading'}</div>
);
...
<Loading condition={props.data && props.data.result && props.data.result.length > 1}>
{() => (
<div> { ViewHelper.getCatalogItems(props.data) }</div>
)}
</Loading>
Notice that since props.children is a function, it's used as children() in ternary expression.
Or use a HOC for components:
const withLoading = (Comp) =>
({ condition, ...props }) => (
<div>{condition ? <Comp {...props} /> : 'Loading'}</div>
)
);
...
const LoadingCatalogItemsComponent = withLoading(CatalogItemsComponent);
the children parameter received in the Loading component will have already rendered in the parent (try logging the content of children from Loading)
getCatalogItems will be called regardless of the conditional
cases where props.data need to be handled here. there are multiple ways to do this:
defaultProps or type checking in general
input validation for getCatalogItems
destructuring assignment
default function parameters
Updated answer: as estus points out below, render props are probably a good way to do this. Here's an example:
import React from "react";
import ReactDOM from "react-dom";
const Loading = ({ condition, render }) => {
if (condition) {
return render();
} else {
return "Loading";
}
};
const Thing = ({ data }) => {
console.log(data);
return data.map(d => <li>{d}</li>);
};
class App extends React.Component {
state = {
data: [1, 2, 3]
};
render() {
return (
<Loading
condition={this.state.data.length > 1}
render={() => {
return <Thing data={this.state.data} />;
}}
/>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
CodeSandbox here.
As #estus said, HOCs and render props are two popular methods. Moving:
<div>{ ViewHelper.getCatalogItems(props.data)}</div>
into its own component (which is passes the prop, e.g., <CatalogItems {...props} />) will also stop you from getting errors. As long as the code isn't in the actual render method; otherwise, it's fired, regardless of whether React would have actually rendered it.
Example:
const Loading = ({ condition, children }) => (
<div>{condition ? children : "Loading in 3 seconds"}</div>
);
// now that it's in its own component the code isn't run until the component actually renders
const CatalogItems = ({ data }) => data.result.map(item => item);
class App extends React.Component {
state = {
data: null
};
// dummy API call
componentDidMount() {
setTimeout(
() => this.setState({ data: { result: ["cat ", "dog ", "mouse "] } }),
3000
);
}
render() {
const props = this.state; // let's just pretend these were inherited props
return (
<Loading
condition={
props.data && props.data.result && props.data.result.length > 1
}
data={props.data}
>
<CatalogItems {...props} />
</Loading>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
<div id='root'></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.3.1/umd/react.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.3.1/umd/react-dom.development.js"></script>
I'm trying to find the proper way to define some components which could be used in a generic way:
<Parent>
<Child value="1">
<Child value="2">
</Parent>
There is a logic going on for rendering between parent and children components of course, you can imagine <select> and <option> as an example of this logic.
This is a dummy implementation for the purpose of the question:
var Parent = React.createClass({
doSomething: function(value) {
},
render: function() {
return (<div>{this.props.children}</div>);
}
});
var Child = React.createClass({
onClick: function() {
this.props.doSomething(this.props.value); // doSomething is undefined
},
render: function() {
return (<div onClick={this.onClick}></div>);
}
});
The question is whenever you use {this.props.children} to define a wrapper component, how do you pass down some property to all its children?
Cloning children with new props
You can use React.Children to iterate over the children, and then clone each element with new props (shallow merged) using React.cloneElement.
See the code comment why I don't recommend this approach.
const Child = ({ childName, sayHello }) => (
<button onClick={() => sayHello(childName)}>{childName}</button>
);
function Parent({ children }) {
// We pass this `sayHello` function into the child elements.
function sayHello(childName) {
console.log(`Hello from ${childName} the child`);
}
const childrenWithProps = React.Children.map(children, child => {
// Checking isValidElement is the safe way and avoids a
// typescript error too.
if (React.isValidElement(child)) {
return React.cloneElement(child, { sayHello });
}
return child;
});
return <div>{childrenWithProps}</div>
}
function App() {
// This approach is less type-safe and Typescript friendly since it
// looks like you're trying to render `Child` without `sayHello`.
// It's also confusing to readers of this code.
return (
<Parent>
<Child childName="Billy" />
<Child childName="Bob" />
</Parent>
);
}
ReactDOM.render(<App />, document.getElementById("container"));
<script src="https://unpkg.com/react#17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom#17/umd/react-dom.production.min.js"></script>
<div id="container"></div>
Calling children as a function
Alternatively, you can pass props to children via render props. In this approach, the children (which can be children or any other prop name) is a function which can accept any arguments you want to pass and returns the actual children:
const Child = ({ childName, sayHello }) => (
<button onClick={() => sayHello(childName)}>{childName}</button>
);
function Parent({ children }) {
function sayHello(childName) {
console.log(`Hello from ${childName} the child`);
}
// `children` of this component must be a function
// which returns the actual children. We can pass
// it args to then pass into them as props (in this
// case we pass `sayHello`).
return <div>{children(sayHello)}</div>
}
function App() {
// sayHello is the arg we passed in Parent, which
// we now pass through to Child.
return (
<Parent>
{(sayHello) => (
<React.Fragment>
<Child childName="Billy" sayHello={sayHello} />
<Child childName="Bob" sayHello={sayHello} />
</React.Fragment>
)}
</Parent>
);
}
ReactDOM.render(<App />, document.getElementById("container"));
<script src="https://unpkg.com/react#17/umd/react.production.min.js"></script>
<script src="https://unpkg.com/react-dom#17/umd/react-dom.production.min.js"></script>
<div id="container"></div>
For a slightly cleaner way to do it, try:
<div>
{React.cloneElement(this.props.children, { loggedIn: this.state.loggedIn })}
</div>
Edit:
To use with multiple individual children (the child must itself be a component) you can do. Tested in 16.8.6
<div>
{React.cloneElement(this.props.children[0], { loggedIn: true, testPropB: true })}
{React.cloneElement(this.props.children[1], { loggedIn: true, testPropA: false })}
</div>
Try this
<div>{React.cloneElement(this.props.children, {...this.props})}</div>
It worked for me using react-15.1.
Use {...this.props} is suggested in https://reactjs.org/docs/jsx-in-depth.html#spread-attributes
Pass props to direct children.
See all other answers
Pass shared, global data through the component tree via context
Context is designed to share data that can be considered “global” for a tree of React components, such as the current authenticated user, theme, or preferred language. 1
Disclaimer: This is an updated answer, the previous one used the old context API
It is based on Consumer / Provide principle. First, create your context
const { Provider, Consumer } = React.createContext(defaultValue);
Then use via
<Provider value={/* some value */}>
{children} /* potential consumers */
</Provider>
and
<Consumer>
{value => /* render something based on the context value */}
</Consumer>
All Consumers that are descendants of a Provider will re-render whenever the Provider’s value prop changes. The propagation from Provider to its descendant Consumers is not subject to the shouldComponentUpdate method, so the Consumer is updated even when an ancestor component bails out of the update. 1
Full example, semi-pseudo code.
import React from 'react';
const { Provider, Consumer } = React.createContext({ color: 'white' });
class App extends React.Component {
constructor(props) {
super(props);
this.state = {
value: { color: 'black' },
};
}
render() {
return (
<Provider value={this.state.value}>
<Toolbar />
</Provider>
);
}
}
class Toolbar extends React.Component {
render() {
return (
<div>
<p> Consumer can be arbitrary levels deep </p>
<Consumer>
{value => <p> The toolbar will be in color {value.color} </p>}
</Consumer>
</div>
);
}
}
1 https://facebook.github.io/react/docs/context.html
Passing Props to Nested Children
With the update to React Hooks you can now use React.createContext and useContext.
import * as React from 'react';
// React.createContext accepts a defaultValue as the first param
const MyContext = React.createContext();
functional Parent(props) {
const doSomething = React.useCallback((value) => {
// Do something here with value
}, []);
return (
<MyContext.Provider value={{ doSomething }}>
{props.children}
</MyContext.Provider>
);
}
function Child(props: { value: number }) {
const myContext = React.useContext(MyContext);
const onClick = React.useCallback(() => {
myContext.doSomething(props.value);
}, [props.value, myContext.doSomething]);
return (
<div onClick={onClick}>{props.value}</div>
);
}
// Example of using Parent and Child
import * as React from 'react';
function SomeComponent() {
return (
<Parent>
<Child value={1} />
<Child value={2} />
</Parent>
);
}
React.createContext shines where React.cloneElement case couldn't handle nested components
function SomeComponent() {
return (
<Parent>
<Child value={1} />
<SomeOtherComp>
<Child value={2} />
</SomeOtherComp>
</Parent>
);
}
The best way, which allows you to make property transfer is children like a function pattern
https://medium.com/merrickchristensen/function-as-child-components-5f3920a9ace9
Code snippet: https://stackblitz.com/edit/react-fcmubc
Example:
const Parent = ({ children }) => {
const somePropsHere = {
style: {
color: "red"
}
// any other props here...
}
return children(somePropsHere)
}
const ChildComponent = props => <h1 {...props}>Hello world!</h1>
const App = () => {
return (
<Parent>
{props => (
<ChildComponent {...props}>
Bla-bla-bla
</ChildComponent>
)}
</Parent>
)
}
You can use React.cloneElement, it's better to know how it works before you start using it in your application. It's introduced in React v0.13, read on for more information, so something along with this work for you:
<div>{React.cloneElement(this.props.children, {...this.props})}</div>
So bring the lines from React documentation for you to understand how it's all working and how you can make use of them:
In React v0.13 RC2 we will introduce a new API, similar to
React.addons.cloneWithProps, with this signature:
React.cloneElement(element, props, ...children);
Unlike cloneWithProps, this new function does not have any magic
built-in behavior for merging style and className for the same reason
we don't have that feature from transferPropsTo. Nobody is sure what
exactly the complete list of magic things are, which makes it
difficult to reason about the code and difficult to reuse when style
has a different signature (e.g. in the upcoming React Native).
React.cloneElement is almost equivalent to:
<element.type {...element.props} {...props}>{children}</element.type>
However, unlike JSX and cloneWithProps, it also preserves refs. This
means that if you get a child with a ref on it, you won't accidentally
steal it from your ancestor. You will get the same ref attached to
your new element.
One common pattern is to map over your children and add a new prop.
There were many issues reported about cloneWithProps losing the ref,
making it harder to reason about your code. Now following the same
pattern with cloneElement will work as expected. For example:
var newChildren = React.Children.map(this.props.children, function(child) {
return React.cloneElement(child, { foo: true })
});
Note: React.cloneElement(child, { ref: 'newRef' }) DOES override the
ref so it is still not possible for two parents to have a ref to the
same child, unless you use callback-refs.
This was a critical feature to get into React 0.13 since props are now
immutable. The upgrade path is often to clone the element, but by
doing so you might lose the ref. Therefore, we needed a nicer upgrade
path here. As we were upgrading callsites at Facebook we realized that
we needed this method. We got the same feedback from the community.
Therefore we decided to make another RC before the final release to
make sure we get this in.
We plan to eventually deprecate React.addons.cloneWithProps. We're not
doing it yet, but this is a good opportunity to start thinking about
your own uses and consider using React.cloneElement instead. We'll be
sure to ship a release with deprecation notices before we actually
remove it so no immediate action is necessary.
more here...
I needed to fix accepted answer above to make it work using that instead of this pointer. This within the scope of map function didn't have doSomething function defined.
var Parent = React.createClass({
doSomething: function() {
console.log('doSomething!');
},
render: function() {
var that = this;
var childrenWithProps = React.Children.map(this.props.children, function(child) {
return React.cloneElement(child, { doSomething: that.doSomething });
});
return <div>{childrenWithProps}</div>
}})
Update: this fix is for ECMAScript 5, in ES6 there is no need in var that=this
Method 1 - clone children
const Parent = (props) => {
const attributeToAddOrReplace= "Some Value"
const childrenWithAdjustedProps = React.Children.map(props.children, child =>
React.cloneElement(child, { attributeToAddOrReplace})
);
return <div>{childrenWithAdjustedProps }</div>
}
Full Demo
Method 2 - use composable context
Context allows you to pass a prop to a deep child component without explicitly passing it as a prop through the components in between.
Context comes with drawbacks:
Data doesn't flow in the regular way - via props.
Using context creates a contract between the consumer and the provider. It might be more difficult to understand and replicate the requirements needed to reuse a component.
Using a composable context
export const Context = createContext<any>(null);
export const ComposableContext = ({ children, ...otherProps }:{children:ReactNode, [x:string]:any}) => {
const context = useContext(Context)
return(
<Context.Provider {...context} value={{...context, ...otherProps}}>{children}</Context.Provider>
);
}
function App() {
return (
<Provider1>
<Provider2>
<Displayer />
</Provider2>
</Provider1>
);
}
const Provider1 =({children}:{children:ReactNode}) => (
<ComposableContext greeting="Hello">{children}</ComposableContext>
)
const Provider2 =({children}:{children:ReactNode}) => (
<ComposableContext name="world">{children}</ComposableContext>
)
const Displayer = () => {
const context = useContext(Context);
return <div>{context.greeting}, {context.name}</div>;
};
None of the answers address the issue of having children that are NOT React components, such as text strings. A workaround could be something like this:
// Render method of Parent component
render(){
let props = {
setAlert : () => {alert("It works")}
};
let childrenWithProps = React.Children.map( this.props.children, function(child) {
if (React.isValidElement(child)){
return React.cloneElement(child, props);
}
return child;
});
return <div>{childrenWithProps}</div>
}
Cleaner way considering one or more children
<div>
{ React.Children.map(this.props.children, child => React.cloneElement(child, {...this.props}))}
</div>
If you have multiple children you want to pass props to, you can do it this way, using the React.Children.map:
render() {
let updatedChildren = React.Children.map(this.props.children,
(child) => {
return React.cloneElement(child, { newProp: newProp });
});
return (
<div>
{ updatedChildren }
</div>
);
}
If your component is having just one child, there's no need for mapping, you can just cloneElement straight away:
render() {
return (
<div>
{
React.cloneElement(this.props.children, {
newProp: newProp
})
}
</div>
);
}
Parent.jsx:
import React from 'react';
const doSomething = value => {};
const Parent = props => (
<div>
{
!props || !props.children
? <div>Loading... (required at least one child)</div>
: !props.children.length
? <props.children.type {...props.children.props} doSomething={doSomething} {...props}>{props.children}</props.children.type>
: props.children.map((child, key) =>
React.cloneElement(child, {...props, key, doSomething}))
}
</div>
);
Child.jsx:
import React from 'react';
/* but better import doSomething right here,
or use some flux store (for example redux library) */
export default ({ doSomething, value }) => (
<div onClick={() => doSomething(value)}/>
);
and main.jsx:
import React from 'react';
import { render } from 'react-dom';
import Parent from './Parent';
import Child from './Child';
render(
<Parent>
<Child/>
<Child value='1'/>
<Child value='2'/>
</Parent>,
document.getElementById('...')
);
see example here: https://plnkr.co/edit/jJHQECrKRrtKlKYRpIWl?p=preview
Got inspired by all the answers above and this is what I have done. I am passing some props like some data, and some components.
import React from "react";
const Parent = ({ children }) => {
const { setCheckoutData } = actions.shop;
const { Input, FieldError } = libraries.theme.components.forms;
const onSubmit = (data) => {
setCheckoutData(data);
};
const childrenWithProps = React.Children.map(
children,
(child) =>
React.cloneElement(child, {
Input: Input,
FieldError: FieldError,
onSubmit: onSubmit,
})
);
return <>{childrenWithProps}</>;
};
Here's my version that works with single, multiple, and invalid children.
const addPropsToChildren = (children, props) => {
const addPropsToChild = (child, props) => {
if (React.isValidElement(child)) {
return React.cloneElement(child, props);
} else {
console.log("Invalid element: ", child);
return child;
}
};
if (Array.isArray(children)) {
return children.map((child, ix) =>
addPropsToChild(child, { key: ix, ...props })
);
} else {
return addPropsToChild(children, props);
}
};
Usage example:
https://codesandbox.io/s/loving-mcclintock-59emq?file=/src/ChildVsChildren.jsx:0-1069
Further to #and_rest answer, this is how I clone the children and add a class.
<div className="parent">
{React.Children.map(this.props.children, child => React.cloneElement(child, {className:'child'}))}
</div>
Maybe you can also find useful this feature, though many people have considered this as an anti-pattern it still can be used if you're know what you're doing and design your solution well.
Function as Child Components
I think a render prop is the appropriate way to handle this scenario
You let the Parent provide the necessary props used in child component, by refactoring the Parent code to look to something like this:
const Parent = ({children}) => {
const doSomething(value) => {}
return children({ doSomething })
}
Then in the child Component you can access the function provided by the parent this way:
class Child extends React {
onClick() => { this.props.doSomething }
render() {
return (<div onClick={this.onClick}></div>);
}
}
Now the fianl stucture will look like this:
<Parent>
{(doSomething) =>
(<Fragment>
<Child value="1" doSomething={doSomething}>
<Child value="2" doSomething={doSomething}>
<Fragment />
)}
</Parent>
The slickest way to do this:
{React.cloneElement(this.props.children, this.props)}
According to the documentation of cloneElement()
React.cloneElement(
element,
[props],
[...children]
)
Clone and return a new React element using element as the starting
point. The resulting element will have the original element’s props
with the new props merged in shallowly. New children will replace
existing children. key and ref from the original element will be
preserved.
React.cloneElement() is almost equivalent to:
<element.type {...element.props} {...props}>{children}</element.type>
However, it also preserves refs. This means that if you get a child
with a ref on it, you won’t accidentally steal it from your ancestor.
You will get the same ref attached to your new element.
So cloneElement is what you would use to provide custom props to the children. However there can be multiple children in the component and you would need to loop over it. What other answers suggest is for you to map over them using React.Children.map. However React.Children.map unlike React.cloneElement changes the keys of the Element appending and extra .$ as the prefix. Check this question for more details: React.cloneElement inside React.Children.map is causing element keys to change
If you wish to avoid it, you should instead go for the forEach function like
render() {
const newElements = [];
React.Children.forEach(this.props.children,
child => newElements.push(
React.cloneElement(
child,
{...this.props, ...customProps}
)
)
)
return (
<div>{newElements}</div>
)
}
You no longer need {this.props.children}. Now you can wrap your child component using render in Route and pass your props as usual:
<BrowserRouter>
<div>
<ul>
<li><Link to="/">Home</Link></li>
<li><Link to="/posts">Posts</Link></li>
<li><Link to="/about">About</Link></li>
</ul>
<hr/>
<Route path="/" exact component={Home} />
<Route path="/posts" render={() => (
<Posts
value1={1}
value2={2}
data={this.state.data}
/>
)} />
<Route path="/about" component={About} />
</div>
</BrowserRouter>
For any one who has a single child element this should do it.
{React.isValidElement(this.props.children)
? React.cloneElement(this.props.children, {
...prop_you_want_to_pass
})
: null}
When using functional components, you will often get the TypeError: Cannot add property myNewProp, object is not extensible error when trying to set new properties on props.children. There is a work around to this by cloning the props and then cloning the child itself with the new props.
const MyParentComponent = (props) => {
return (
<div className='whatever'>
{props.children.map((child) => {
const newProps = { ...child.props }
// set new props here on newProps
newProps.myNewProp = 'something'
const preparedChild = { ...child, props: newProps }
return preparedChild
})}
</div>
)
}
Is this what you required?
var Parent = React.createClass({
doSomething: function(value) {
}
render: function() {
return <div>
<Child doSome={this.doSomething} />
</div>
}
})
var Child = React.createClass({
onClick:function() {
this.props.doSome(value); // doSomething is undefined
},
render: function() {
return <div onClick={this.onClick}></div>
}
})
I came to this post while researching for a similar need, but i felt cloning solution that is so popular, to be too raw and takes my focus away from the functionality.
I found an article in react documents Higher Order Components
Here is my sample:
import React from 'react';
const withForm = (ViewComponent) => {
return (props) => {
const myParam = "Custom param";
return (
<>
<div style={{border:"2px solid black", margin:"10px"}}>
<div>this is poc form</div>
<div>
<ViewComponent myParam={myParam} {...props}></ViewComponent>
</div>
</div>
</>
)
}
}
export default withForm;
const pocQuickView = (props) => {
return (
<div style={{border:"1px solid grey"}}>
<div>this is poc quick view and it is meant to show when mouse hovers over a link</div>
</div>
)
}
export default withForm(pocQuickView);
For me i found a flexible solution in implementing the pattern of Higher Order Components.
Of course it depends on the functionality, but it is good if someone else is looking for a similar requirement, it is much better than being dependent on raw level react code like cloning.
Other pattern that i actively use is the container pattern. do read about it, there are many articles out there.
In case anyone is wondering how to do this properly in TypeScript where there are one or multiple child nodes. I am using the uuid library to generate unique key attributes for the child elements which, of course, you don't need if you're only cloning one element.
export type TParentGroup = {
value?: string;
children: React.ReactElement[] | React.ReactElement;
};
export const Parent = ({
value = '',
children,
}: TParentGroup): React.ReactElement => (
<div className={styles.ParentGroup}>
{Array.isArray(children)
? children.map((child) =>
React.cloneElement(child, { key: uuidv4(), value })
)
: React.cloneElement(children, { value })}
</div>
);
As you can see, this solution takes care of rendering an array of or a single ReactElement, and even allows you to pass properties down to the child component(s) as needed.
Some reason React.children was not working for me. This is what worked for me.
I wanted to just add a class to the child. similar to changing a prop
var newChildren = this.props.children.map((child) => {
const className = "MenuTooltip-item " + child.props.className;
return React.cloneElement(child, { className });
});
return <div>{newChildren}</div>;
The trick here is the React.cloneElement. You can pass any prop in a similar manner
Render props is most accurate approach to this problem. Instead of passing the child component to parent component as children props, let parent render child component manually. Render is built-in props in react, which takes function parameter. In this function you can let parent component render whatever you want with custom parameters. Basically it does the same thing as child props but it is more customizable.
class Child extends React.Component {
render() {
return <div className="Child">
Child
<p onClick={this.props.doSomething}>Click me</p>
{this.props.a}
</div>;
}
}
class Parent extends React.Component {
doSomething(){
alert("Parent talks");
}
render() {
return <div className="Parent">
Parent
{this.props.render({
anythingToPassChildren:1,
doSomething: this.doSomething})}
</div>;
}
}
class Application extends React.Component {
render() {
return <div>
<Parent render={
props => <Child {...props} />
}/>
</div>;
}
}
Example at codepen
There are lot of ways to do this.
You can pass children as props in parent.
example 1 :
function Parent({ChildElement}){
return <ChildElement propName={propValue} />
}
return <Parent ChildElement={ChildComponent}/>
Pass children as Function
example 2 :
function Parent({children}){
return children({className: "my_div"})
}
OR
function Parent({children}){
let Child = children
return <Child className='my_div' />
}
function Child(props){
return <div {...props}></div>
}
export <Parent>{props => <Child {...props} />}</Parent>
I did struggle to have the listed answers work but failed. Eventually, I found out that the issue is with correctly setting up the parent-child relationship. Merely nesting components inside other components does not mean that there is a parent-child relationship.
Example 1. Parent-child relationship;
function Wrapper() {
return (
<div>
<OuterComponent>
<InnerComponent />
</OuterComponent>
</div>
);
}
function OuterComponent(props) {
return props.children;
}
function InnerComponent() {
return <div>Hi! I'm in inner component!</div>;
}
export default Wrapper;
Example 2. Nested components:
function Wrapper() {
return (
<div>
<OuterComponent />
</div>
);
}
function OuterComponent(props) {
return <InnerComponent />
}
function InnerComponent() {
return <div>Hi! I'm in inner component!</div>;
}
export default Wrapper;
As I said above, props passing works in Example 1 case.
The article below explains it https://medium.com/#justynazet/passing-props-to-props-children-using-react-cloneelement-and-render-props-pattern-896da70b24f6