I currently have an HOC component that I'd like to port over to use react hooks and basically just start thinking in that idea.
This HOC component basically provides a functionality for a wrapped component to display an alert dialog box. The HOC component manages its own state making this very easy for the wrapped component to display an alert dialog. The wrapped component simply has to call the function passed down to props to display it.
Here's what the HOC looks like now:
function withAlertDialog(WrappedComponent) {
return class extends Component {
constructor(props) {
super(props);
this.state = {
alertDialogOpen: false,
alertMessage: ""
};
}
displayAlert = message => {
this.setState({alertDialogOpen: true, alertMessage: message});
}
closeAlertDialog = () => {
this.setState({alertDialogOpen: false});
}
render() {
return (
<React.Fragment>
<WrappedComponent
onDisplayAlert={this.displayAlert}
onCloseAlert={this.closeAlertDialog} />
<MyAlertDialogComponent
open={this.state.alertDialogOpen}
onClose={this.closeAlertDialog} />
</React.Fragment>
);
}
}
}
This is a more simple case, the actual HOC used is a lot more complex, but the idea still follows. The wrapped component can now basically call this.props.onDisplayAlert('some message here'); to display the alert. The wrapped component also doesn't have to render the MyAlertDialogComponent in its own render function. Basically, the wrapped component does not have to worry about how MyAlertDialogComponent is handled, all it knows is that calling this.props.onDisplayAlert will display an alert dialog box somehow. Reusing this HOC saves a lot of lines of code.
How would one go about changing this to a react hooks implementation? I've tried looking around but most articles and the documentation itself use an HOC with a single wrapped component and isn't really managing another component in addition to that. I'd like to understand how to change to the "react hooks" ideology but keep that same level of convenience about not having to render MyAlertDialogComponent in each component that wants to use it.
The only difference between your old HOC and a new HOC utilizing hooks is that you simply have to change the anonymous class you return from your HOC to an anonymous function that uses hooks.
Conversion between a class and a hooked-in function follows normal conversion rules that you might find in numerous tutorials online. In the case of your example, convert your state to useState and convert your class methods to regular functions.
You just pass the state and these regular functions around to whatever component needs them. Calling the setter for your state will re-render the component.
If you review the example below you'll see MyWrappedComponent is wrapped using withAlertDialog which passes the two function props to MyWrappedComponent. Those functions are used inside MyWrappedComponent to set the state that renders MyAlertDialogComponent
const { useState } = React
function withAlertDialog(WrappedComponent) {
return function(props){
const [alertState, setAlertState] = useState({
alertDialogOpen: false,
alertMessage: ""
})
const displayAlert = message => {
setAlertState({
alertDialogOpen: true,
alertMessage: message
});
}
const closeAlertDialog = () => {
setAlertState({alertDialogOpen: false});
}
return (
<React.Fragment>
<WrappedComponent
onDisplayAlert={displayAlert}
onCloseAlert={closeAlertDialog} />
<MyAlertDialogComponent
open={alertState.alertDialogOpen}
onClose={closeAlertDialog} />
</React.Fragment>
);
}
}
const MyWrappedComponent = withAlertDialog(function (props){
return (
<div>
<a onClick={props.onDisplayAlert}>Open Alert</a>
<a onClick={props.onCloseAlert}>Close Alert</a>
</div>
)
})
function MyAlertDialogComponent(props){
if(!props.open){
return null
}
return (
<div>Dialogue Open</div>
)
}
function App(){
return (
<MyWrappedComponent />
)
}
ReactDOM.render(<App />, document.querySelector('#app'))
div > a {
display : block;
padding : 10px 0;
}
<div id="app" />
<script crossorigin src="https://unpkg.com/react#16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#16/umd/react-dom.production.min.js"></script>
We should avoid method binding inside render because during re-rendering it will create the new methods instead of using the old one, that will affect the performance.
So for the scenarios like this:
<input onChange = { this._handleChange.bind(this) } ...../>
We can bind _handleChange method either in constructor:
this._handleChange = this._handleChange.bind(this);
Or we can use property initializer syntax:
_handleChange = () => {....}
Now lets consider the case where we want to pass some extra parameter, lets say in a simple todo app, onclick of item i need to delete the item from array, for that i need to pass either the item index or the todo name in each onClick method:
todos.map(el => <div key={el} onClick={this._deleteTodo.bind(this, el)}> {el} </div>)
For now just assume that todo names are unique.
As per DOC:
The problem with this syntax is that a different callback is created
each time the component renders.
Question:
How to avoid this way of binding inside render method or what are the alternatives of this?
Kindly provide any reference or example, thanks.
First: A simple solution will be to create a component for the content inside a map function and pass the values as props and when you call the function from the child component you can pass the value to the function passed down as props.
Parent
deleteTodo = (val) => {
console.log(val)
}
todos.map(el =>
<MyComponent val={el} onClick={this.deleteTodo}/>
)
MyComponent
class MyComponent extends React.Component {
deleteTodo = () => {
this.props.onClick(this.props.val);
}
render() {
return <div onClick={this.deleteTodo}> {this.props.val} </div>
}
}
Sample snippet
class Parent extends React.Component {
_deleteTodo = (val) => {
console.log(val)
}
render() {
var todos = ['a', 'b', 'c'];
return (
<div>{todos.map(el =>
<MyComponent key={el} val={el} onClick={this._deleteTodo}/>
)}</div>
)
}
}
class MyComponent extends React.Component {
_deleteTodo = () => {
console.log('here'); this.props.onClick(this.props.val);
}
render() {
return <div onClick={this._deleteTodo}> {this.props.val} </div>
}
}
ReactDOM.render(<Parent/>, document.getElementById('app'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>
EDIT:
Second: The other approach to it would be to use memoize and return a function
constructor() {
super();
this._deleteTodoListener = _.memoize(
this._deleteTodo, (element) => {
return element.hashCode();
}
)
}
_deleteTodo = (element) => {
//delete handling here
}
and using it like
todos.map(el => <div key={el} onClick={this._deleteTodoListener(el)}> {el} </div>)
P.S. However this is not a best solution and will still result in
multiple functions being created but is still an improvement over the
initial case.
Third: However a more appropriate solution to this will be to add an attribute to the topmost div and get the value from event like
_deleteTodo = (e) => {
console.log(e.currentTarget.getAttribute('data-value'));
}
todos.map(el => <div key={el} data-value={el} onClick={this._deleteTodo}> {el} </div>)
However, in this case the attributes are converted to string using toString method and hence and object will be converted to [Object Object] and and array like ["1" , "2", "3"] as "1, 2, 3"
How to avoid this way of binding inside render method or what are the
alternatives of this?
If you care about re-rendering then shouldComponentUpdate and PureComponent are your friends and they will help you optimize rendering.
You have to extract "Child" component from the "Parent" and pass always the same props and implement shouldComponentUpdate or use PureComponent. What we want is a case when we remove a child, other children shouldn't be re-rendered.
Example
import React, { Component, PureComponent } from 'react';
import { render } from 'react-dom';
class Product extends PureComponent {
render() {
const { id, name, onDelete } = this.props;
console.log(`<Product id=${id} /> render()`);
return (
<li>
{id} - {name}
<button onClick={() => onDelete(id)}>Delete</button>
</li>
);
}
}
class App extends Component {
constructor(props) {
super(props);
this.state = {
products: [
{ id: 1, name: 'Foo' },
{ id: 2, name: 'Bar' },
],
};
this.handleDelete = this.handleDelete.bind(this);
}
handleDelete(productId) {
this.setState(prevState => ({
products: prevState.products.filter(product => product.id !== productId),
}));
}
render() {
console.log(`<App /> render()`);
return (
<div>
<h1>Products</h1>
<ul>
{
this.state.products.map(product => (
<Product
key={product.id}
onDelete={this.handleDelete}
{...product}
/>
))
}
</ul>
</div>
);
}
}
render(<App />, document.getElementById('root'));
Demo: https://codesandbox.io/s/99nZGlyZ
Expected behaviour
<App /> render()
<Product id=1... render()
<Product id=2... render()
When we remove <Product id=2 ... only <App /> is re-rendered.
render()
To see those messages in demo, open the dev tools console.
The same technique is used and described in article: React is Slow, React is Fast: Optimizing React Apps in Practice by François Zaninotto.
Documentation encourages to use data-attributes and access them from within evt.target.dataset:
_deleteTodo = (evt) => {
const elementToDelete = evt.target.dataset.el;
this.setState(prevState => ({
todos: prevState.todos.filter(el => el !== elementToDelete)
}))
}
// and from render:
todos.map(
el => <div key={el} data-el={el} onClick={this._deleteTodo}> {el} </div>
)
Also note that this makes sense only when you have performance issues:
Is it OK to use arrow functions in render methods?
Generally speaking, yes, it is OK, and it is often the easiest way to
pass parameters to callback functions.
If you do have performance issues, by all means, optimize!
This answer https://stackoverflow.com/a/45053753/2808062 is definitely exhaustive, but I'd say fighting excessive re-renders instead of just re-creating the tiny callback would bring you more performance improvements. That's normally achieved by implementing a proper shouldComponentUpdate in the child component.
Even if the props are exactly the same, the following code will still re-render children unless they prevent it in their own shouldComponentUpdate (they might inherit it from PureComponent):
handleChildClick = itemId => {}
render() {
return this.props.array.map(itemData => <Child onClick={this.handleChildClick} data={itemData})
}
Proof: https://jsfiddle.net/69z2wepo/92281/.
So, in order to avoid re-renders, the child component has to implement shouldComponentUpdate anyway. Now, the only reasonable implementation is completely ignoring onClick regardless of whether it has changed:
shouldComponentUpdate(nextProps) {
return this.props.array !== nextProps.array;
}
For the rare times when you need a reference to another JSX element in React, you can use the ref prop, like this:
class Widget extends React.PureComponent {
example() {
// do something
}
render() {
...
<Widget ref={r => this.mywidget = r}/>
<OtherWidget onClick={e => this.mywidget.example()}/>
Here, the Widget instance is stored in this.mywidget for later use, and the example() function can be called on it.
In Material UI, you can wrap components around a withTheme() call to make the theme accessible in their props:
export default withTheme()(Widget);
However if this is done, the ref receives an instance of WithTheme rather than Widget. This means the example() function is no longer accessible.
Is there some way to use ref with a component wrapped by withTheme() so that the underlying object can still be accessed, in the same manner as if withTheme() had not been used?
Here is an example demonstrating the issue. Lines 27 and 28 can be commented/uncommented to see that things only fail when the withTheme() call is added.
In order to get the ref of the component which is wrapped with withStyles, you can create a wrapper around Widget, and use that with withStyles like
const WithRefWidget = ({ innerRef, ...rest }) => {
console.log(innerRef);
return <Widget ref={innerRef} {...rest} />;
};
const MyWidget = withTheme()(WithRefWidget);
class Demo extends React.PureComponent {
constructor(props) {
super(props);
this.mywidget = null;
}
render() {
return (
<React.Fragment>
<MyWidget
innerRef={r => {
console.log(r);
this.mywidget = r;
}}
/>
<Button
onClick={e => {
e.preventDefault();
console.log(this.mywidget);
}}
variant="raised"
>
Click
</Button>
</React.Fragment>
);
}
}
Have a look at this answer to see an other alternative approach
losing functions when using recompose component as ref
This is a shorter alternative based on Shubham Khatri's answer. That answer works when you can't alter the inner component, this example is a bit shorter when you can modify the inner component.
Essentially ref doesn't get passed through withTheme() so you have to use a prop with a different name, and implement ref functionality on it yourself:
class Widget extends React.PureComponent {
constructor(props) {
props.ref2(this); // duplicate 'ref' functionality for the 'ref2' prop
...
const MyWidget = withTheme()(Widget);
...
<MyWidget
ref2={r => {
console.log(r);
this.mywidget = r;
}}
/>
So I know that you can access a component's children with this.props.children:
<MyComponent>
<span>Bob</span>
<span>Sally</span>
</MyComponent>
Which is great if I'm interested in Bob and Sally, but what if I want to interact with the components that make up MyComponent (i.e. Subcomp1 and Subcomp2 shown below)?
render: function() {
return (
<div className="my-comp">
<Subcomp1 />
<Subcomp2 />
</div>
);
},
Use Case
I'm trying to create a higher order component that manages the tab index (roving tab index: https://www.w3.org/TR/wai-aria-practices/#kbd_roving_tabindex) of the wrapped component's sub-components, so it would be great if I could get a ref to the wrapped component and filter it's subcomponents by type.
So far the only approach that seems possible is to have each component store a ref for each of it's subcomponents, but this is tedious and kind of defeats the purpose of an HOC. Is there a generic way to access these sub-components?
A rough example of what I'm trying to do:
var HOC = (ComposedComponent) => {
return React.createClass({
componentDidMount: function() {
const subComponents = this.composedComponent.subComponents; // Something like this would be nice
const menuItems = subComponents.filter(() => {
// figure out a way to identify components of a certain type
});
this.applyRovingTabIndex(menuItems);
},
render: function() {
return (
<ComposedComponent
ref={(c) => { this.composedComponent = c }}
{...this.props} />
);
}
});
};
The tabIndex manipulation need not be done in the HOC, rather it can be done in the Parent component that renders all the HOCs. Because all you need is to determine which sub component is clicked and adjust the selected state on the Parent component. This selected state can then be propagated back to the sub components who compare their index with selected index and assign tabIndex accordingly.
You can send the respective props to determine whether the current ComposedComponent is selected or not by passing an onClick event handler all the way. Then in your sub component you can access tabIndex using this.props.tabIndex and render your parent div as
<div tabIndex={this.props.tabIndex}> </div>
The code below is almost like pseudo code to give an idea. If you feel that this does not solve your requirement you can try out a Tab example worked out by an awesome developer at this link CODEPEN EXAMPLE
const HOC = (ComposedComponent) => {
return class extends React.Component {
render (
<ComposedComponent
tabIndex={this.props.selected === this.props.index ? "0" : "-1"}
{...this.props}
/>
)
}
}
class Parent extends React.Component {
state = {
selected: 0
}
// Set the current selection based on the currentSelection argument
// that is bound to the function as it is sent along to Props
adjustTabIndices = (currentSelection) => (event) => {
this.setState({selection: currentSelection})
}
render {
return (
<div>
{
// These are your various MenuItem components that
// you want to compose using HOC
[MenuItem1, MenuItem2, MenuItem3].map(index => {
const MenuItem = HOC(MenuItem1);
return (
<MenuItem
key={index}
onClick={this.adjustTabIndices(index)}
selection={this.state.selected}
index={index}
/>
)
})
}
</div>
)
}
}
Suppose I have a React class P, which renders two child classes, C1 and C2.
C1 contains an input field. I'll refer to this input field as Foo.
My goal is to let C2 react to changes in Foo.
I've come up with two solutions, but neither of them feels quite right.
First solution:
Assign P a state, state.input.
Create an onChange function in P, which takes in an event and sets state.input.
Pass this onChange to C1 as a props, and let C1 bind this.props.onChange to the onChange of Foo.
This works. Whenever the value of Foo changes, it triggers a setState in P, so P will have the input to pass to C2.
But it doesn't feel quite right for the same reason: I'm setting the state of a parent element from a child element. This seems to betray the design principle of React: single-direction data flow.
Is this how I'm supposed to do it, or is there a more React-natural solution?
Second solution:
Just put Foo in P.
But is this a design principle I should follow when I structure my app—putting all form elements in the render of the highest-level class?
Like in my example, if I have a large rendering of C1, I really don't want to put the whole render of C1 to render of P just because C1 has a form element.
How should I do it?
So, if I'm understanding you correctly, your first solution is suggesting that you're keeping state in your root component? I can't speak for the creators of React, but generally, I find this to be a proper solution.
Maintaining state is one of the reasons (at least I think) that React was created. If you've ever implemented your own state pattern client side for dealing with a dynamic UI that has a lot of interdependent moving pieces, then you'll love React, because it alleviates a lot of this state management pain.
By keeping state further up in the hierarchy, and updating it through eventing, your data flow is still pretty much unidirectional, you're just responding to events in the Root component, you're not really getting the data there via two way binding, you're telling the Root component that "hey, something happened down here, check out the values" or you're passing the state of some data in the child component up in order to update the state. You changed the state in C1, and you want C2 to be aware of it, so, by updating the state in the Root component and re-rendering, C2's props are now in sync since the state was updated in the Root component and passed along.
class Example extends React.Component {
constructor (props) {
super(props)
this.state = { data: 'test' }
}
render () {
return (
<div>
<C1 onUpdate={this.onUpdate.bind(this)}/>
<C2 data={this.state.data}/>
</div>
)
}
onUpdate (data) { this.setState({ data }) }
}
class C1 extends React.Component {
render () {
return (
<div>
<input type='text' ref='myInput'/>
<input type='button' onClick={this.update.bind(this)} value='Update C2'/>
</div>
)
}
update () {
this.props.onUpdate(this.refs.myInput.getDOMNode().value)
}
})
class C2 extends React.Component {
render () {
return <div>{this.props.data}</div>
}
})
ReactDOM.renderComponent(<Example/>, document.body)
Having used React to build an app now, I'd like to share some thoughts to this question I asked half a year ago.
I recommend you to read
Thinking in React
Flux
The first post is extremely helpful to understanding how you should structure your React app.
Flux answers the question why should you structure your React app this way (as opposed to how to structure it). React is only 50% of the system, and with Flux you get to see the whole picture and see how they constitute a coherent system.
Back to the question.
As for my first solution, it is totally OK to let the handler go the reverse direction, as the data is still going single-direction.
However, whether letting a handler trigger a setState in P can be right or wrong depending on your situation.
If the app is a simple Markdown converter, C1 being the raw input and C2 being the HTML output, it's OK to let C1 trigger a setState in P, but some might argue this is not the recommended way to do it.
However, if the app is a todo list, C1 being the input for creating a new todo, C2 the todo list in HTML, you probably want to handler to go two level up than P -- to the dispatcher, which let the store update the data store, which then send the data to P and populate the views. See that Flux article. Here is an example: Flux - TodoMVC
Generally, I prefer the way described in the todo list example. The less state you have in your app the better.
Five years later with introduction of React Hooks there is now much more elegant way of doing it with use useContext hook.
You define context in a global scope, export variables, objects and functions in the parent component and then wrap children in the App in a context provided and import whatever you need in child components. Below is a proof of concept.
import React, { useState, useContext } from "react";
import ReactDOM from "react-dom";
import styles from "./styles.css";
// Create context container in a global scope so it can be visible by every component
const ContextContainer = React.createContext(null);
const initialAppState = {
selected: "Nothing"
};
function App() {
// The app has a state variable and update handler
const [appState, updateAppState] = useState(initialAppState);
return (
<div>
<h1>Passing state between components</h1>
{/*
This is a context provider. We wrap in it any children that might want to access
App's variables.
In 'value' you can pass as many objects, functions as you want.
We wanna share appState and its handler with child components,
*/}
<ContextContainer.Provider value={{ appState, updateAppState }}>
{/* Here we load some child components */}
<Book title="GoT" price="10" />
<DebugNotice />
</ContextContainer.Provider>
</div>
);
}
// Child component Book
function Book(props) {
// Inside the child component you can import whatever the context provider allows.
// Earlier we passed value={{ appState, updateAppState }}
// In this child we need the appState and the update handler
const { appState, updateAppState } = useContext(ContextContainer);
function handleCommentChange(e) {
//Here on button click we call updateAppState as we would normally do in the App
// It adds/updates comment property with input value to the appState
updateAppState({ ...appState, comment: e.target.value });
}
return (
<div className="book">
<h2>{props.title}</h2>
<p>${props.price}</p>
<input
type="text"
//Controlled Component. Value is reverse vound the value of the variable in state
value={appState.comment}
onChange={handleCommentChange}
/>
<br />
<button
type="button"
// Here on button click we call updateAppState as we would normally do in the app
onClick={() => updateAppState({ ...appState, selected: props.title })}
>
Select This Book
</button>
</div>
);
}
// Just another child component
function DebugNotice() {
// Inside the child component you can import whatever the context provider allows.
// Earlier we passed value={{ appState, updateAppState }}
// but in this child we only need the appState to display its value
const { appState } = useContext(ContextContainer);
/* Here we pretty print the current state of the appState */
return (
<div className="state">
<h2>appState</h2>
<pre>{JSON.stringify(appState, null, 2)}</pre>
</div>
);
}
const rootElement = document.body;
ReactDOM.render(<App />, rootElement);
You can run this example in the Code Sandbox editor.
The first solution, with keeping the state in parent component, is the correct one. However, for more complex problems, you should think about some state management library, redux is the most popular one used with react.
I'm surprised that there are no answers with a straightforward idiomatic React solution at the moment I'm writing. So here's the one (compare the size and complexity to others):
class P extends React.Component {
state = { foo : "" };
render(){
const { foo } = this.state;
return (
<div>
<C1 value={ foo } onChange={ x => this.setState({ foo : x })} />
<C2 value={ foo } />
</div>
)
}
}
const C1 = ({ value, onChange }) => (
<input type="text"
value={ value }
onChange={ e => onChange( e.target.value ) } />
);
const C2 = ({ value }) => (
<div>Reacting on value change: { value }</div>
);
I'm setting the state of a parent element from a child element. This seems to betray the design principle of React: single-direction data flow.
Any controlled input (idiomatic way of working with forms in React) updates the parent state in its onChange callback and still doesn't betray anything.
Look carefully at C1 component, for instance. Do you see any significant difference in the way how C1 and built-in input component handle the state changes? You should not, because there is none. Lifting up the state and passing down value/onChange pairs is idiomatic for raw React. Not usage of refs, as some answers suggest.
More recent answer with an example, which uses React.useState
Keeping the state in the parent component is the recommended way. The parent needs to have an access to it as it manages it across two children components. Moving it to the global state, like the one managed by Redux, is not recommended for same same reason why global variable is worse than local in general in software engineering.
When the state is in the parent component, the child can mutate it if the parent gives the child value and onChange handler in props (sometimes it is called value link or state link pattern). Here is how you would do it with hooks:
function Parent() {
var [state, setState] = React.useState('initial input value');
return <>
<Child1 value={state} onChange={(v) => setState(v)} />
<Child2 value={state}>
</>
}
function Child1(props) {
return <input
value={props.value}
onChange={e => props.onChange(e.target.value)}
/>
}
function Child2(props) {
return <p>Content of the state {props.value}</p>
}
The whole parent component will re-render on input change in the child, which might be not an issue if the parent component is small / fast to re-render. The re-render performance of the parent component still can be an issue in the general case (for example large forms). This is solved problem in your case (see below).
State link pattern and no parent re-render are easier to implement using the 3rd party library, like Hookstate - supercharged React.useState to cover variety of use cases, including your's one. (Disclaimer: I am an author of the project).
Here is how it would look like with Hookstate. Child1 will change the input, Child2 will react to it. Parent will hold the state but will not re-render on state change, only Child1 and Child2 will.
import { useStateLink } from '#hookstate/core';
function Parent() {
var state = useStateLink('initial input value');
return <>
<Child1 state={state} />
<Child2 state={state}>
</>
}
function Child1(props) {
// to avoid parent re-render use local state,
// could use `props.state` instead of `state` below instead
var state = useStateLink(props.state)
return <input
value={state.get()}
onChange={e => state.set(e.target.value)}
/>
}
function Child2(props) {
// to avoid parent re-render use local state,
// could use `props.state` instead of `state` below instead
var state = useStateLink(props.state)
return <p>Content of the state {state.get()}</p>
}
PS: there are many more examples here covering similar and more complicated scenarios, including deeply nested data, state validation, global state with setState hook, etc. There is also complete sample application online, which uses the Hookstate and the technique explained above.
You should learn Redux and ReactRedux library.It will structure your states and props in one store and you can access them later in your components .
With React >= 16.3 you can use ref and forwardRef, to gain access to child's DOM from its parent. Don't use old way of refs anymore.
Here is the example using your case :
import React, { Component } from 'react';
export default class P extends React.Component {
constructor (props) {
super(props)
this.state = {data: 'test' }
this.onUpdate = this.onUpdate.bind(this)
this.ref = React.createRef();
}
onUpdate(data) {
this.setState({data : this.ref.current.value})
}
render () {
return (
<div>
<C1 ref={this.ref} onUpdate={this.onUpdate}/>
<C2 data={this.state.data}/>
</div>
)
}
}
const C1 = React.forwardRef((props, ref) => (
<div>
<input type='text' ref={ref} onChange={props.onUpdate} />
</div>
));
class C2 extends React.Component {
render () {
return <div>C2 reacts : {this.props.data}</div>
}
}
See Refs and ForwardRef for detailed info about refs and forwardRef.
The right thing to do is to have the state in the parent component, to avoid ref and what not
An issue is to avoid constantly updating all children when typing into a field
Therefore, each child should be a Component (as in not a PureComponent) and implement shouldComponentUpdate(nextProps, nextState)
This way, when typing into a form field, only that field updates
The code below uses #bound annotations from ES.Next babel-plugin-transform-decorators-legacy of BabelJS 6 and class-properties (the annotation sets this value on member functions similar to bind):
/*
© 2017-present Harald Rudell <harald.rudell#gmail.com> (http://www.haraldrudell.com)
All rights reserved.
*/
import React, {Component} from 'react'
import {bound} from 'class-bind'
const m = 'Form'
export default class Parent extends Component {
state = {one: 'One', two: 'Two'}
#bound submit(e) {
e.preventDefault()
const values = {...this.state}
console.log(`${m}.submit:`, values)
}
#bound fieldUpdate({name, value}) {
this.setState({[name]: value})
}
render() {
console.log(`${m}.render`)
const {state, fieldUpdate, submit} = this
const p = {fieldUpdate}
return (
<form onSubmit={submit}> {/* loop removed for clarity */}
<Child name='one' value={state.one} {...p} />
<Child name='two' value={state.two} {...p} />
<input type="submit" />
</form>
)
}
}
class Child extends Component {
value = this.props.value
#bound update(e) {
const {value} = e.target
const {name, fieldUpdate} = this.props
fieldUpdate({name, value})
}
shouldComponentUpdate(nextProps) {
const {value} = nextProps
const doRender = value !== this.value
if (doRender) this.value = value
return doRender
}
render() {
console.log(`Child${this.props.name}.render`)
const {value} = this.props
const p = {value}
return <input {...p} onChange={this.update} />
}
}
The concept of passing data from parent to child and vice versa is explained.
import React, { Component } from "react";
import ReactDOM from "react-dom";
// taken refrence from https://gist.github.com/sebkouba/a5ac75153ef8d8827b98
//example to show how to send value between parent and child
// props is the data which is passed to the child component from the parent component
class Parent extends Component {
constructor(props) {
super(props);
this.state = {
fieldVal: ""
};
}
onUpdateParent = val => {
this.setState({
fieldVal: val
});
};
render() {
return (
// To achieve the child-parent communication, we can send a function
// as a Prop to the child component. This function should do whatever
// it needs to in the component e.g change the state of some property.
//we are passing the function onUpdateParent to the child
<div>
<h2>Parent</h2>
Value in Parent Component State: {this.state.fieldVal}
<br />
<Child onUpdate={this.onUpdateParent} />
<br />
<OtherChild passedVal={this.state.fieldVal} />
</div>
);
}
}
class Child extends Component {
constructor(props) {
super(props);
this.state = {
fieldValChild: ""
};
}
updateValues = e => {
console.log(e.target.value);
this.props.onUpdate(e.target.value);
// onUpdateParent would be passed here and would result
// into onUpdateParent(e.target.value) as it will replace this.props.onUpdate
//with itself.
this.setState({ fieldValChild: e.target.value });
};
render() {
return (
<div>
<h4>Child</h4>
<input
type="text"
placeholder="type here"
onChange={this.updateValues}
value={this.state.fieldVal}
/>
</div>
);
}
}
class OtherChild extends Component {
render() {
return (
<div>
<h4>OtherChild</h4>
Value in OtherChild Props: {this.props.passedVal}
<h5>
the child can directly get the passed value from parent by this.props{" "}
</h5>
</div>
);
}
}
ReactDOM.render(<Parent />, document.getElementById("root"));