So I keep div element in my state. I want to change it's className in response to onClick event. I know I could do it with event.target.className but the code below is only the sample of a biggest application and it's not possible to use it there. As a resultant from changeClass function I get
"TypeError: Cannot assign to read only property 'className' of object '#'".
So I wonder is there any other way to do it?
import React, { Component } from "react";
import "./styles/style.css";
class App extends Component {
constructor(props) {
super(props);
this.state = {
myDiv: [
<div
id="firstDiv"
key={1}
className={"first"}
onClick={this.changeClass}
/>
]
};
}
changeClass = () => {
this.setState(prevState => {
return { myDiv: (prevState.myDiv[0].props.className = "second") };
});
};
render() {
return <div>{this.state.myDiv.map(div => div)}</div>;
}
}
export default App;
Don't put your jsx in state. only add className and state and onChangeClass use this.stateState to update className.
import React, { Component } from "react";
import "./styles/style.css";
class App extends Component {
constructor(props) {
super(props);
this.state = {
className:"first"
};
}
changeClass = () => {
this.setState({ classNmae: "two" });
};
render() {
return <div>
<div
id="firstDiv"
className={this.state.className}
onClick={this.changeClass}
/>
</div>;
}
}
export default App;
there's a simpler option try this:
import React, { Component } from "react";
import "./styles/style.css";
class App extends Component {
constructor(props) {
super(props);
this.state = {
className: "first"
};
}
changeClass = () => {
this.setState({className: "second"});
};
render() {
return <div
id="firstDiv"
className={this.state.className}
onClick={this.changeClass}>
</div>;
}
}
export default App;
You can use Hooks if you use a React version upper than 16.8
import React, { useState } from "react"
import "./styles/style.css"
const App = () => {
const [myClass, setMyClass] = useState("first")
const changeClass = () => {
setMyClass("second")
}
render() {
return <div
id="firstDiv"
className={myClass}
onClick={changeClass}>
</div>;
}
}
export default App
Related
I am having an issue where I'm trying to pass a function(updateEvents) via props from my App.js file to a NumberOfEvents.js file. I passed the same function to another component with no issues. However, when I try on the NumberOfEvents file, I get the following error:
Error image
Please help!!!
Here is the Parent:
import React, { Component } from 'react';
import EventList from './EventList';
import CitySearch from './CitySearch';
import NumberOfEvents from './NumberOfEvents';
import { extractLocations, getEvents } from './api';
import './nprogress.css';
import './App.css';
class App extends Component {
state = {
events: [],
locations: [],
numberOfEvents: 32
}
componentDidMount() {
this.mounted = true;
getEvents().then((events) => {
if (this.mounted) {
this.setState({
events: events.slice(0, this.state.numberOfEvents),
locations: extractLocations(events)
});
}
});
}
componentWillUnmount() {
this.mounted = false;
}
updateEvents = (location, eventCount) => {
this.mounted = true;
getEvents().then((events) => {
const locationEvents = (location === 'all')
? events
: events.filter((event) => event.location === location);
this.setState({
events: locationEvents,
numberOfEvents: eventCount,
});
});
};
render() {
return (
<div className="App">
<CitySearch
locations={this.state.locations} updateEvents={this.updateEvents} />
<EventList
events={this.state.events} />
<NumberOfEvents
numberOfEvents={this.state.numberOfEvents}
updateEvents={this.updateEvents} />
</div>
);
}
}
export default App;
And here is the Child:
import React, { Component } from 'react';
class NumberOfEvents extends Component {
state = {
numberOfEvents: 32
}
handleChange = (event) => {
const value = event.target.value;
this.setState({
numberOfEvents: value,
});
this.props.updateEvents('', value);
};
render() {
return (
<input
className="number"
value={this.state.numberOfEvents}
onChange={this.handleChange} />
)
}
}
export default NumberOfEvents;
Im not sure this will help ...In Your Parent Component , inside return statement when passing the updateEvents Prop, try passing it as arrow function like this ....
updateEvents={ () => this.updateEvents() } />
try adding a constructor to the child component
constructor(props) {
super(props);
this.state = {
numberOfEvents: 32
}
}
I am trying to get adaptValue from Component1 and use it in Component2. For some reason this does not work since my adaptValue is always null/undefined. Is it because Parent is a functional component?
const Parent = (props) => {
const [adaptValue, setAdapt] = useState(null);
return (
<div>
<Component1 setAdapt={setAdapt}/>
<Component2 adaptValue={adaptValue}/>
</div>
)
}
export default class Component1 extends Component {
constructor(props) {
super(props);
}
adaptValue = (value) =>{
DO_SOMETHING_WITH_VALUE
}
componentDidMount() {
this.props.setAdapt(this.adaptValue);
}
render() {
return something;
}
}
export default class Component2 extends Component {
constructor(props) {
super(props);
}
someFunction = (value) =>{
...
//adaptValue is always undefined
this.props.adaptValue(value)
...
}
render() {
return something;
}
}
UPDATE Made the parent a class component in the end and all works. Wondering whether this is a compatibility issue between functional or class-based components.
When passing setAdapt to Component1 ... setAdapt is already a function. There is no need to wrap it in another one. Component1 will modify the value, and Component2 will display it. Function Components have nothing to do with the behavior.
Try ...
App.js
import React, { useState } from "react";
import "./styles.css";
import Component1 from "./Component1";
import Component2 from "./Component2";
export default function App() {
const [adaptValue, setAdapt] = useState(null);
return (
<div>
<Component1 setAdapt={setAdapt} />
<Component2 adaptValue={adaptValue} />
</div>
);
}
Component1.js
import React, { Component } from "react";
export default class Component1 extends Component {
handleClick = () => {
this.props.setAdapt("New Value");
};
render() {
return <button onClick={() => this.handleClick()}>Set Value</button>;
}
}
Component2.js
import React, { Component } from "react";
export default class Component2 extends Component {
render() {
return !!this.props.adaptValue ? (
<h1>{`"${this.props.adaptValue}" <- Value of adaptValue`}</h1>
) : (
<h1>adaptValue Not Assigned</h1>
);
}
}
Sandbox Example ...
In my react app I am using a timer component. I want this component to run in the background and call a parent function after a certain time. The code is giving error. My code is
parent component
import React, { Component } from 'react';
import Timer from './timer';
class Parent extends Component {
finish(){
console.log('fininsh')
}
render() {
return (
<div>
<Timer data={this.finish.bind(this)} />
</div>
);
}
}
export default Parent;
timer component
import React, { Component } from 'react';
class Timer extends Component {
constructor(props){
super(props);
this.state = {
fin: false
}
}
componentDidMount(){
this.myInterval = setInterval(() => {
this.setState({fin: true})
}, 10000);
}
childfinish = () => {
this.props.data.finish
}
render() {
const {fin} = this.state;
if(fin){
return(
<div>
{this.childfinish};
</div>
)
} else {
return (
<div>
<h1>Counting...</h1>
</div>
)
}
}
}
export default Timer;
the error is
Expected an assignment or function call and instead saw an expression
data prop does not contain function finish().
Remove {this.childfinish} from render() and
componentDidMount(){
this.myInterval = setInterval(() => {
this.setState({fin: true})
this.props.data();
}, 10000);
}
Found the solution
parent component
import React, { Component } from 'react';
import Timer from './timer';
class Parent extends Component {
finish(){
console.log('fininsh')
}
render() {
return (
<div>
<Timer data={{callfinish : this.finish.bind(this)}} />
</div>
);
}
}
export default Parent;
Child Component
import React, { Component } from 'react';
class Timer extends Component {
constructor(props){
super(props);
this.state = {
fin: false
}
}
componentDidMount(){
this.myInterval = setInterval(() => {
this.setState({fin: true})
}, 10000);
}
childfinish = () => {
clearInterval(this.myInterval);
this.props.data.callfinish();
}
render() {
const {fin} = this.state;
if(fin){
this.childfinish();
return (
<div></div>
)
} else {
return (
<div>
<h1>Counting...</h1>
</div>
)
}
}
}
export default Timer;
The parent function will run after 10 seconds.
Is there any way to send data from the component's state to HoC?
My component
import React, { Component } from 'react';
import withHandleError from './withHandleError';
class SendScreen extends Component {
contructor() {
super();
this.state = {
error: true
}
}
render() {
return (
<div> Test </div>
)
}
};
export default withHandleError(SendScreen)
My HoC component:
import React, { Component } from 'react';
import { ErrorScreen } from '../../ErrorScreen';
import { View } from 'react-native';
export default Cmp => {
return class extends Component {
render() {
const { ...rest } = this.props;
console.log(this.state.error) //// Cannot read property 'error' of null
if (error) {
return <ErrorScreen />
}
return <Cmp { ...rest } />
}
}
}
Is there any way to do this?
Is the only option is to provide props that must come to the SendScreen component from outside??
A parent isn't aware of child's state. While it can get an instance of a child with a ref and access state, it can't watch on state updates, the necessity to do this indicates design problem.
This is the case for lifting up the state. A parent needs to be notified that there was an error:
export default Cmp => {
return class extends Component {
this.state = {
error: false
}
onError() = () => this.setState({ error: true });
render() {
if (error) {
return <ErrorScreen />
}
return <Cmp onError={this.onError} { ...this.props } />
}
}
}
export default withHandleError(data)(SendScreen)
In data you can send the value you want to pass to HOC, and can access as prop.
I know I answer late, but my answer can help other people
It is very easy to do.
WrappedComponent
import React, {Component} from 'react';
import PropTypes from 'prop-types';
import HocComponent from './HocComponent';
const propTypes = {
passToHOC: PropTypes.func,
};
class WrappedComponent extends Component {
constructor(props) {
super(props);
this.state = {
error: true,
};
}
componentDidMount() {
const {passToHOC} = this.props;
const {error} = this.state;
passToHOC(error); // <--- pass the <<error>> to the HOC component
}
render() {
return <div> Test </div>;
}
}
WrappedComponent.propTypes = propTypes;
export default HocComponent(WrappedComponent);
HOC Component
import React, {Component} from 'react';
export default WrappedComponent => {
return class extends Component {
constructor() {
super();
this.state = {
error: false,
};
}
doAnything = error => {
console.log(error); //<-- <<error === true>> from child component
this.setState({error});
};
render() {
const {error} = this.state;
if (error) {
return <div> ***error*** passed successfully</div>;
}
return <WrappedComponent {...this.props} passToHOC={this.doAnything} />;
}
};
};
React docs: https://reactjs.org/docs/lifting-state-up.html
import React, { Component } from 'react';
import withHandleError from './withHandleError';
class SendScreen extends Component {
contructor() {
super();
this.state = {
error: true
}
}
render() {
return (
<div state={...this.state}> Test </div>
)
}
};
export default withHandleError(SendScreen)
You can pass the state as a prop in your component.
The component I am trying to render:
import React, { Component } from 'react';
export default class QueryPrint extends Component {
render() {
console.log('working');
return (
<div>Hello</div>
)
}
}
The component that is trying to call it:
import React, { Component } from 'react';
import { connect } from 'react-redux';
import {
Button,
} from 'reactstrap';
import QueryPrint from './bq_print';
class QueryResults extends Component {
constructor(props) {
super(props);
this.print = this.print.bind(this);
}
print() {
console.log('Clicked');
return (
<QueryPrint />
);
}
render() {
return (
<Button
className='cuts-btn'
color='success'
onClick={this.print}
>
Print
</Button>
)
}
}
function mapStateToProps(state) {
return {
query_data: state.results.query_data
}
}
export default connect (mapStateToProps, null)(QueryResults);
The console.log('clicked') is working, but the component that is supposed to render in that method doesn't--no console.log('working') or <div>.
Returning something from a click callback has no effect. If you want to render something, you do so in the render method. The click callback's job is to call this.setState(), which will then kick off a render.
Perhaps something like this:
class QueryResults extends Component {
constructor(props) {
super(props);
this.print = this.print.bind(this);
this.state = {
queryPrint: false,
}
}
print() {
console.log('Clicked');
this.setState({ queryPrint: true })
}
render() {
const { queryPrint } = this.state;
return (
<React.Fragment>
{queryPrint && <QueryPrint />}
<Button
className='cuts-btn'
color='success'
onClick={this.print}
>
Print
</Button>
</React.Fragment>
)
}
}
React Native works differently. It is more like a web app - you need to navigate to the other component.
Look at this example its very to the point: https://facebook.github.io/react-native/docs/navigation
Alternatively if you want to make only part of the screen change you will need to include it into your own render and control it thru a flag or a state machine.
https://facebook.github.io/react-native/docs/direct-manipulation