I learned that you could use HOC to only modify the render function when the class logic is the same. I try to do it myself and came up with a solution using this.props.children and cloneElement instead.
I searched on StackOverFlow to find differences between the 2 but the only question about this is from 2016 and React changed since. I was wondering if there is performance issues with one or the other and in 2019 what would be considered "best practice"
Here's with cloneElement:
<Counter>
<ButtonCounter />
</Counter>
<Counter>
<KeyStrokesCounter />
</Counter>
export default class Counter extends Component {
constructor(props) {
super(props);
this.state = {
counter: 0
};
}
updateCounter = () => {
this.setState(prev => ({
counter: prev.counter + 1
}));
};
render() {
return (
<React.Fragment>
{React.cloneElement(this.props.children, {
clickHandler: this.updateCounter,
counter: this.state.counter
})}
</React.Fragment>
);
}
}
export default class ButtonCounter extends Component {
constructor(props) {
super(props);
console.log('ButtonCounter created lol');
}
render() {
return (
<div>
<button onClick={this.props.clickHandler}>
Clicked {this.props.counter} times
</button>
</div>
);
}
}
And HOC:
<Button />
<InputKeyStroke />
const CounterComponent = OgComp => {
class NewComp extends React.Component {
constructor(props) {
super(props);
this.state = {
counter: 42
};
}
incrementCounter = () => {
this.setState(prev => ({
counter: prev.counter + 1
}));
};
render() {
return (
<OgComp
evtHandler={this.incrementCounter}
counter={this.state.counter}
/>
);
}
}
return NewComp;
};
export default CounterComponent;
export default CounterComponent(
class Button extends React.Component {
constructor(props) {
super(props);
console.log('RCONST BUTTON');
}
render() {
return (
<button onClick={this.props.evtHandler}>
Clicked {this.props.counter} times
</button>
);
}
}
);
Is there a best way to do this? The constructor isn't called during each cloneElement event.
This doesn't answer your question but here's a benchmark I found for cloneElement VS render props: https://gist.github.com/nemoDreamer/21412b28dc65d51e2c5c8561a8f82ce1
Related
i was learning react from 'React docs' for few days and today i got into the trouble. Link to docs: https://reactjs.org/docs/conditional-rendering.html#element-variables.
Exercise is that when the button clicks text will change. In docs, they did it with functions and it works perfectly but i tried it with classes.
The problem is that state doesn't update when props changes, it only have its initial value. I'm struggling with it since 2 hours and didn't find the solution. I'm new to React so please be forbearance.
Code:
class UserGreeting extends React.Component {
render() {
return (
<h1>Welcome back!</h1>
);
}
}
class GuestGreeting extends React.Component {
render() {
return (
<h1>Please sign up!</h1>
);
}
}
class Greeting extends React.Component {
constructor(props) {
super(props);
this.state = {isLoggedIn: this.props.isLoggedIn};
}
render() {
let isLoggedIn = this.state.isLoggedIn;
if (isLoggedIn) {
return <UserGreeting />;
}
return <GuestGreeting />;
}
}
class LoginButton extends React.Component {
constructor(props) {
super(props);
this.state = {onClick: this.props.onClick};
}
render() {
return (
<button onClick={this.state.onClick}>Login</button>
);
}
}
class LogoutButton extends React.Component {
constructor(props) {
super(props);
this.state = {onClick: this.props.onClick};
}
render() {
return (
<button onClick={this.state.onClick}>Logout</button>
);
}
}
class LoginControl extends React.Component {
constructor(props) {
super(props);
this.state = {isLoggedIn: true};
}
handleLoginClick = () => {
this.setState({isLoggedIn: true});
}
handleLogoutClick = () => {
this.setState({isLoggedIn: false});
}
render() {
const isLoggedIn = this.state.isLoggedIn;
let button;
if (isLoggedIn) {
button = <LogoutButton onClick={this.handleLogoutClick} />;
} else {
button = <LoginButton onClick={this.handleLoginClick} />;
}
return (
<div>
<Greeting isLoggedIn={isLoggedIn} />
{button}
</div>
);
}
}
ReactDOM.render(
<LoginControl />,
document.getElementById('root')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
<div id="root"></div>
You are storing your answer in the state in the Greeting component inside the constructor. The constructor will only be called once at mount component.
Change your Greeting component with below code**
class Greeting extends React.Component {
render() {
let isLoggedIn = this.props.isLoggedIn;
if (isLoggedIn) {
return <UserGreeting />;
}
return <GuestGreeting />;
}
}
How do I call a child component function from the parent component? I've tried using refs but I can't get it to work. I get errors like, Cannot read property 'handleFilterByClass' of undefined.
Path: Parent Component
export default class StudentPage extends React.Component {
constructor(props) {
super(props);
this.state = {
};
}
newStudentUserCreated() {
console.log('newStudentUserCreated1');
this.refs.studentTable.handleTableUpdate();
}
render() {
return (
<div>
<StudentTable
studentUserProfiles={this.props.studentUserProfiles}
ref={this.studentTable}
/>
</div>
);
}
}
Path: StudentTable
export default class StudentTable extends React.Component {
constructor(props) {
super(props);
this.state = {
studentUserProfiles: props.studentUserProfiles,
};
this.handleTableUpdate = this.handleTableUpdate.bind(this);
}
handleTableUpdate = () => (event) => {
// Do stuff
}
render() {
return (
<div>
// stuff
</div>
);
}
}
UPDATE
Path StudentContainer
export default StudentContainer = withTracker(() => {
const addStudentContainerHandle = Meteor.subscribe('companyAdmin.addStudentContainer.userProfiles');
const loadingaddStudentContainerHandle = !addStudentContainerHandle.ready();
const studentUserProfiles = UserProfiles.find({ student: { $exists: true } }, { sort: { lastName: 1, firstName: 1 } }).fetch();
const studentUserProfilesExist = !loadingaddStudentContainerHandle && !!studentUserProfiles;
return {
studentUserProfiles: studentUserProfilesExist ? studentUserProfiles : [],
};
})(StudentPage);
My design here is: component (Child 1) creates a new studentProfile. Parent component is notified ... which then tells component (Child 2) to run a function to update the state of the table data.
I'm paraphrasing the OP's comment here but it seems the basic idea is for a child component to update a sibling child.
One solution is to use refs.
In this solution we have the Parent pass a function to ChildOne via props. When ChildOne calls this function the Parent then via a ref calls ChildTwo's updateTable function.
Docs: https://reactjs.org/docs/refs-and-the-dom.html
Demo (open console to view result): https://codesandbox.io/s/9102103xjo
class Parent extends React.Component {
constructor(props) {
super(props);
this.childTwo = React.createRef();
}
newUserCreated = () => {
this.childTwo.current.updateTable();
};
render() {
return (
<div className="App">
<ChildOne newUserCreated={this.newUserCreated} />
<ChildTwo ref={this.childTwo} />
</div>
);
}
}
class ChildOne extends React.Component {
handleSubmit = () => {
this.props.newUserCreated();
};
render() {
return <button onClick={this.handleSubmit}>Submit</button>;
}
}
class ChildTwo extends React.Component {
updateTable() {
console.log("Update Table");
}
render() {
return <div />;
}
}
I have 2 Components one called NodeWidget and another called PopupWidget. In the NodeWidget it has a Model assigned to it which looks like the following:
PopupModel
export class PopupModel {
question: string;
model: string;
constructor(question: string, model: string) {
this.question = question;
this.model = model;
}
}
The parent Component is NodeWidget which passes in the Model to the PopupWidget with data in.
NodeWidget
{ this.state.showComponent ?
<PopupWidget model={this.props.popupModel} /> :
null
}
Then finally in the child Component we have this code:
export interface PopupWidgetProps {
model: PopupModel;
}
export interface PopupWidgetState { }
export class PopupWidget extends React.Component<PopupWidgetProps, PopupWidgetState> {
constructor(props: PopupWidgetProps) {
super(props);
this.state = { };
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
console.log(this.props);
}
render() {
return (
<div className="popup">
<div className="popup_inner">
<h1>TEST</h1>
<input type="text" value={this.props.model.question} placeholder="Write a question..." />
<button onClick={this.handleClick}>close me</button>
</div>
</div>
);
}
}
I want to be able to bind the value of the input to the model and then for it to update the original model in the Parent Component, am i doing this correctly as it does not seem to work.
You can do this to pass the input result to parent component on the button click:
PopupWidget :
export class PopupWidget extends React.Component<PopupWidgetProps, PopupWidgetState> {
constructor(props: PopupWidgetProps) {
super(props);
this.state = { question: '' };
this.handleClick = this.handleClick.bind(this);
}
handleClick() {
this.props.inputResult(this.state.question)
}
render() {
return (
<div className="popup">
<div className="popup_inner">
<h1>TEST</h1>
<input type="text" value={this.state.question} onChange={(question) => { this.setState({ question })}} placeholder="Write a question..." />
<button onClick={this.handleClick}>close me</button>
</div>
</div>
);
}
}
NodeWidget :
constructor(props) {
super(props);
this.getInputResult = this.getInputResult.bind(this);
}
getInputResult(question) {
this.props.inputResult(question);
this.setState({ showComponent: false });
}
...
{ this.state.showComponent ?
<PopupWidget inputResult={this.getInputResult} /> :
null
}
Finally in PopupModel (i assume this is a react component, i don't know if you can work with simple es6 class in react):
export class PopupModel extends React.Component {
constructor(props) {
this.state = { question: '', model: '' }; // set your initial state
this.getInputResult = this.getInputResult.bind(this);
}
getInputResult(question) {
this.setState({ question }); // here's our result from the input
}
render(){
return(<NodeWidget inputResult={this.getInputResult} />);
}
}
This can be pretty boring to handle if you have multiple components between the two which have to communicate.
You can use a HOC like Redux or MobX to handle an app state that can be passed in any component, and any component can dispatch actions to update the app state, you should go for it if you have multiple cases like this.
I have a react component(parent) that has as state another react component(child)
The parent passes down is't state as props to the child.
But if I do setState on the passed down property, it does not update in the child.How do I make such that a change in state is reflected in the child?
See code:
class Child extends React.Component {
constructor(props) {
super(props)
}
render() {
return (
<div>
{this.props.x}
</div>
)
}
}
class Parent extends React.Component {
constructor(props) {
super(props)
this.state = {x: 1, intervalID: 0, currentScreen: <Child x={0} />}
}
componentDidMount() {
let self = this
let intervalID = setInterval(function() {
self.setState({x: self.state.x+1})
}, 1000)
self.setState({intervalID: intervalID, currentScreen: <Child x={self.state.x} />})
}
render() {
return (
<div>
{this.state.currentScreen}
</div>
)
}
}
ReactDOM.render(<Parent />, document.getElementById('app'))
Below code is working.
import React from 'react';
import ReactDOM from 'react-dom';
class Child extends React.Component {
render() {
return (
<div>
{this.props.x}
</div>
)
}
}
class Parent extends React.Component {
constructor(props) {
super(props)
this.state = {x: 1, intervalID: 0, currentScreen: <Child x={0} />}
}
componentDidMount() {
let intervalID = setInterval(() => {
const x = this.state.x + 1;
this.setState({
x: x,
currentScreen: <Child x={x} />
});
}, 1000)
this.setState({intervalID: intervalID, currentScreen: <Child x={this.state.x} />})
}
render() {
return (
<div>
{this.state.currentScreen}
</div>
)
}
}
ReactDOM.render(<Parent />, document.getElementById('root'))
Your child component is not updating because for the lifecycle of parent component componentDidMount is only called once when it is being mounted.
If you need to update your state on regular interval you can do something like :
import React, { Component } from 'react';
import { render } from 'react-dom';
class Child extends Component {
constructor(props) {
super(props)
}
render() {
return (
<div>
{this.props.x}
</div>
)
}
}
class Parent extends Component {
constructor(props) {
super(props)
this.state = { x: 1, intervalID: 0 }
}
componentDidMount() {
let self = this
let intervalID = setInterval(function () {
self.setState({ x: self.state.x + 1 })
}, 1000)
self.setState({ intervalID: intervalID })
}
render() {
return (
<div>
<Child x={this.state.x}/>
</div>
)
}
}
render(<Parent />, document.getElementById('root'))
for your case, just so when setState is done, it will call render again and it will pass the latest value of x to the child component.
You can check out live working example on stackblitz
It is a bad practise to maintain JSX in the state. Move all your JSX into the render() and use state variables to manage the state as shown below (For brevity only the Parent component code is shown).
Further instead of doing let self=this use the arrow function for clarity.
Note that you need to use the updater function when setting the state if your new state depends on the previous state. This is because React does batch updates for state. More information can be found in the official documentation.
class Parent extends React.Component {
constructor(props) {
super(props)
this.state = { x: 1 }
}
componentDidMount() {
setInterval(() => {
this.setState((prevState, props) => {
return { x: prevState.x + 1 };
});
},3000)
}
render() {
return (
<div>
<Child x={this.state.x} />
</div>
)
}
}
ReactDOM.render(<Parent />, document.getElementById('root'))
Above function will update the value of x every 3 seconds. Below is a working example
https://codesandbox.io/s/2677zoo4p
In React I am trying to make a button increment a value stored in state.
However using the code below function my value is set undefined or NaN when using handleClick.
class QuestionList extends React.Component {
constructor(props) {
super(props);
this.state = {value: 0};
// This binding is necessary to make `this` work in the callback
this.handleClick = this.handleClick.bind(this);
}
handleClick = (prevState) => {
this.setState({value: prevState.value + 1});
console.log(this.state.value)
}
Can you tell me why this is happening? it should be correct according to the docs here:
https://facebook.github.io/react/docs/state-and-lifecycle.html
Because you are using the handleClick function incorrectly. Here:
handleClick = (prevState) => { .... }
prevState will be an event object passed to handleClick function, you need to use prevState with setState, like this:
handleClick = () => {
this.setState(prevState => {
return {count: prevState.count + 1}
})
}
Another issue is, setState is async so console.log(this.state.value) will not print the updated state value, you need to use callback function with setState.
Check more details about async behaviour of setState and how to check updated value.
Check the working solution:
class App extends React.Component {
constructor(props){
super(props);
this.state={ count: 1}
}
onclick(type){
this.setState(prevState => {
return {count: type == 'add' ? prevState.count + 1: prevState.count - 1}
});
}
render() {
return (
<div>
Count: {this.state.count}
<br/>
<div style={{marginTop: '100px'}}/>
<input type='button' onClick={this.onclick.bind(this, 'add')} value='Inc'/>
<input type='button' onClick={this.onclick.bind(this, 'sub')} value='Dec'/>
</div>
)
}
}
ReactDOM.render(
<App />,
document.getElementById('container')
);
<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='container'></div>
set state is async so you wont see the value update when the console.log happens. You should have the state value printed out on the UI so you can see whats happening. To fix the console log try this.
class QuestionList extends React.Component {
constructor(props) {
super(props);
this.state = {value: 0};
}
handleClick = (prevState) => {
this.setState({value: prevState.value + 1}, () => {
console.log(this.state.value)
});
}
NOTE: when you define an inline lambda (arrow function) for a react class this is bound correctly so you dont need to bind it in the constructor.
also you can change the way you pass the previous number if its just a state increment like this
handleClick = () => {
this.setState({value: this.state.value + 1}, () => {
console.log(this.state.value)
});
}
Hello there, try these codes to increment your value
class Counter extends React.Component{
constructor(props){
super(props);
this.addOne = this.addOne.bind(this);
this.state = {
count : 0
}
}
addOne() { // addOne as HandleClick
this.setState((preState) => {
return {
count : preState.count + 1
};
});
}
render() {
return (
<div>
<h1>Count : {this.state.count}</h1>
<button onClick={this.addOne}>+1</button>
</div>
);
}
}
ReactDOM.render(<Counter />, document.getElementById('YOUR-ID'));
class SkuVariantList extends React.Component {
constructor(props) {
super(props)
this.state = {
clicks: 0
};
this.clickHandler = this.clickHandler.bind(this)
}
componentDidMount() {
this.refs.myComponentDiv.addEventListener('click', this.clickHandler);
}
componentWillUnmount() {
//this.refs.myComponentDiv.removeEventListener('click', this.clickHandler);
}
clickHandler() {
var clk = this.state.clicks
this.setState({
clicks: clk + 1
});
}
render() {
let children = this.props.children;
return (
<div className="my-component" ref="myComponentDiv">
<h2>My Component ({this.state.clicks} clicks})</h2>
<h3>{this.props.headerText}</h3>
{children}
</div>
);
}
}
Try this out
class QuestionList extends React.component {
constructor(props){
super(props)
this.state = {
value : 0
}
}
handleClick(){
this.setState({
value : this.state.value + 1
})
}
render(){
return( <button type="button" onClick={this.handleClick.bind(this)}> {this.state.value} </button> )
}
}
Note that when you set a state, it triggers the render function, which will reflect the current state. Try it out in the browser!
import React from 'react'
class App extends React.Component{
constructor(){
super()
this.state = {
count: 0
}
this.handleClick = this.handleClick.bind(this)
}
handleClick(){
this.setState(prevState => {
return {
count: prevState.count + 1
}
})
}
render(){
return(
<div style = {{display: 'flex', fontSize: 30, flexDirection: 'column', alignItems:'center'}}>
<h1>{this.state.count}</h1>
<button onClick = {this.handleClick}>Change</button>
</div>
)
}
}
export default App
This is the shortest code for that. First, initialize the state, then perform a method to increment.
state = {
counter: 0
}
increaseHandler = () => {
let counter = this.state.counter
counter += 1
this.setState({counter: counter})
}
You can do it this way also where we do both increment and decrement operation with same function making it more modular and redable
class CounterApp extends React.Component{
constructor(){
super();
//here count is initially assigned with 0
this.state ={
count:0
}
}
//when we click Increment or Decrement +1 or -1 is passed to step and the value gets changed it gets updated to the view
increment = (step) =>{
this.setState({
count:this.state.count + step
})
}
render(){
const { count } = this.state;//same as const count = this.state.count;
return(
<div>
<div className="counter-app">
<h2 className="value">{count}</h2>
<button onClick={() => this.increment(+1)}>Increment</button>
<button onClick={() => this.increment(-1)}>Decrement</button>
</div>
</div>
)
}
}