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How do I access a React Class method from outside?

Lets say I have a component defined like this -
// actioncomponent.js
import React from 'react';
class ActionComponent extends React.Component {
state = {
isAction: false;
}
doAction = () => {
this.setState({isAction: true})
}
render () {
return (
<div>
Some render stuff..
</div>
)
}
}
export default ActionComponent
From another completely different file I want to set the state for the first component without rendering it in the new file so I need not use refs or props.
// newfile.js
import ActionComponent from './actioncomponent.js'
ActionComponent.doAction()
I'm aware the doAction can't be exported and calling it static doesn't have access to state either. How do I achieve something like this?

In React ecosystem you probably don't need this.
You can pass this method to a child component:
class ActionComponent extends React.Component {
state = {
isAction: false
}
doAction = () => {
this.setState({isAction: true})
}
render () {
return (
<div>
<Child doAction={this.doAction} />
</div>
)
}
}
And then in a Child component you can fire this action
// ...
render() {
<button onClick={() => props.doAction()}>Test</button>
}
If you need to fire action on parent, instead of child you might want to structure your state on upper level, or lift state up.
You can also achieve similar goal without drilling props, but you'll need some state management tool, e.g. Redux or in some cases Context API would be a great fit.

React/Preact: how to temporarily avoid updating the DOM for a certain component?

I'm using server-side rendering with Webpack's code-splitting. The server returns the HTML for the component. However, when React initializes, since I'm using code-splitting, the React component I want to render isn't downloaded yet. Typically, I'd want to display a loading screen. However, the HTML for the component is already rendered, so I don't want to replace it with a loading screen.
Is there a way to get React to temporarily ignore the component and not update the DOM?
The component looks something like this:
export default class SomeRoute extends Preact.Component {
constructor() {
super();
this.state = {
Component: null,
};
}
componentDidMount() {
if (!this.state.component) {
this.props.componentLoader().then(Component => this.setState({ Component }));
}
}
render({}, { Component }) {
if (!Component) {
return (
<p>Loading...</p>
);
}
return (
<Component />
);
}
}
The output of <Component /> is already returned by the server.

You can use shouldComponentUpdate(). When you return false it will not update the component.
shouldCompnentUpdate(nextprops,nextstate){
return Boolean(this.state.Component)
}

Fetch data only once per React component

I have a simple component that fetches data and only then displays it:
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
loaded: false
stuff: null
};
}
componentDidMount() {
// load stuff
fetch( { path: '/load/stuff' } ).then( stuff => {
this.setState({
loaded: true,
stuff: stuff
});
} );
}
render() {
if ( !this.state.loaded ) {
// not loaded yet
return false;
}
// display component based on loaded stuff
return (
<SomeControl>
{ this.state.stuff.map( ( item, index ) =>
<h1>items with stuff</h1>
) }
</SomeControl>
);
}
}
Each instance of MyComponent loads the same data from the same URL and I need to somehow store it to avoid duplicate requests to the server.
For example, if I have 10 MyComponent on page - there should be just one request (1 fetch).
My question is what's the correct way to store such data? Should I use static variable? Or I need to use two different components?
Thanks for advice!

For people trying to figure it out using functional component.
If you only want to fetch the data on mount then you can add an empty array as attribute to useEffect
So it would be :
useEffect( () => { yourFetch and set }, []) //Empty array for deps.

You should rather consider using state management library like redux, where you can store all the application state and the components who need data can subscribe to. You can call fetch just one time maybe in the root component of the app and all 10 instances of your component can subscribe to state.

If you want to avoid using redux or some kind of state management library, you can import a file which does the fetching for you. Something along these lines. Essentially the cache is stored within the fetcher.js file. When you import the file, it's not actually imported as separate code every time, so the cache variable is consistent between imports. On the first request, the cache is set to the Promise; on followup requests the Promise is just returned.
// fetcher.js
let cache = null;
export default function makeRequest() {
if (!cache) {
cache = fetch({
path: '/load/stuff'
});
}
return cache;
}
// index.js
import fetcher from './fetcher.js';
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
loaded: false
stuff: null
};
}
componentDidMount() {
// load stuff
fetcher().then( stuff => {
this.setState({
loaded: true,
stuff: stuff
});
} );
}
render() {
if ( !this.state.loaded ) {
// not loaded yet
return false;
}
// display component based on loaded stuff
return (
<SomeControl>
{ this.state.stuff.map( ( item, index ) =>
<h1>items with stuff</h1>
) }
</SomeControl>
);
}
}

You can use something like the following code to join active requests into one promise:
const f = (cache) => (o) => {
const cached = cache.get(o.path);
if (cached) {
return cached;
}
const p = fetch(o.path).then((result) => {
cache.delete(o.path);
return result;
});
cache.set(o.path, p);
return p;
};
export default f(new Map());//use Map as caching

If you want to simulate the single fetch call with using react only. Then You can use Provider Consumer API from react context API. There you can make only one api call in provider and can use the data in your components.
const YourContext = React.createContext({});//instead of blacnk object you can have array also depending on your data type of response
const { Provider, Consumer } = YourContext
class ProviderComponent extends React.Component {
componentDidMount() {
//make your api call here and and set the value in state
fetch("your/url").then((res) => {
this.setState({
value: res,
})
})
}
render() {
<Provider value={this.state.value}>
{this.props.children}
</Provider>
}
}
export {
Provider,
Consumer,
}
At some top level you can wrap your Page component inside Provider. Like this
<Provider>
<YourParentComponent />
</Provider>
In your components where you want to use your data. You can something like this kind of setup
import { Consumer } from "path to the file having definition of provider and consumer"
<Consumer>
{stuff => <SomeControl>
{ stuff.map( ( item, index ) =>
<h1>items with stuff</h1>
) }
</SomeControl>
}
</Consumer>
The more convenient way is to use some kind of state manager like redux or mobx. You can explore those options also. You can read about Contexts here
link to context react website
Note: This is psuedo code. for exact implementation , refer the link
mentioned above

If your use case suggests that you may have 10 of these components on the page, then I think your second option is the answer - two components. One component for fetching data and rendering children based on the data, and the second component to receive data and render it.
This is the basis for “smart” and “dumb” components. Smart components know how to fetch data and perform operations with those data, while dumb components simply render data given to them. It seems to me that the component you’ve specified above is too smart for its own good.

ReactJS: I can not get the state to update with API data when the asynchronous API data fetch is completed

I am having a bit of an issue rendering components before the state is set to the data from a returned asynchronous API request. I have a fetch() method that fires off, returns data from an API, and then sets the state to this data. Here is that block of code that handles this:
class App extends Component {
constructor() {
super();
this.state = {
currentPrice: null,
};
}
componentDidMount() {
const getCurrentPrice = () => {
const url = 'https://api.coindesk.com/v1/bpi/currentprice.json';
fetch(url).then(data => data.json())
.then(currentPrice => {
this.setState = ({
currentPrice: currentPrice.bpi.USD.rate
})
console.log('API CALL', currentPrice.bpi.USD.rate);
}).catch((error) => {
console.log(error);
})
}
getCurrentPrice();
}
You will notice the console.log('API CALL', currentPrice.bpi.USD.rate) that I use to check if the API data is being returned, and it absolutely is. currentPrice.bpi.USD.rate returns an integer (2345.55 for example) right in the console as expected.
Great, so then I assumed that
this.setState = ({ currentPrice: currentPrice.bpi.USD.rate }) should set the state without an issue, since this data was received back successfully.
So I now render the components like so:
render() {
return (
<div>
<NavigationBar />
<PriceOverview data={this.state.currentPrice}/>
</div>
);
}
}
export default App;
With this, I was expecting to be able to access this data in my PriceOverview.js component like so: this.props.data
I have used console.log() to check this.props.data inside my PriceOverview.js component, and I am getting 'null' back as that is the default I set intially. The issue I am having is that the components render before the API fetch has ran it's course and updated the state with the returned data. So when App.js renders the PriceOverview.js component, it only passes currentPrice: null to it, because the asynchronous fetch() has not returned the data prior to rendering.
My confusion lies with this.setState. I have read that React will call render any time this.setState is called. So in my mind, once the fetch() request comes back, it calls this.setState and changes the state to the returned data. This in turn should cause a re-render and the new state data should be available. I would be lying if I didn't say I was confused here. I was assuming that once the fetch() returned, it would update the state with the requested data, and then that would trigger a re-render.
There has to be something obvious that I am missing here, but my inexperience leaves me alone.. cold.. in the dark throws of despair. I don't have an issue working with 'hard coded' data, as I can pass that around just fine without worry of when it returns. For example, if I set the state in App.js to this.state = { currentPrice: [254.55] }, then I can access it in PriceOverview.js via this.props.data with zero issue. It's the async API request that is getting me here, and I am afraid it has gotten the best of me tonight.
Here App.js in full:
import React, { Component } from 'react';
import './components/css/App.css';
import NavigationBar from './components/NavigationBar';
import PriceOverview from './components/PriceOverview';
class App extends Component {
constructor() {
super();
this.state = {
currentPrice: null,
};
}
componentDidMount() {
const getCurrentPrice = () => {
const url = 'https://api.coindesk.com/v1/bpi/currentprice.json';
fetch(url).then(data => data.json())
.then(currentPrice => {
this.setState = ({
currentPrice: currentPrice.bpi.USD.rate
})
console.log('API CALL', currentPrice.bpi);
}).catch((error) => {
console.log(error);
})
}
getCurrentPrice();
}
render() {
return (
<div>
<NavigationBar />
<PriceOverview data={this.state.currentPrice}/>
</div>
);
}
}
export default App;
Here is PriceOverview.js in full:
import React, { Component } from 'react';
import './css/PriceOverview.css';
import bitcoinLogo from './assets/bitcoin.svg';
class PriceOverview extends Component {
constructor(props) {
super(props);
this.state = {
currentPrice: this.props.data
}
}
render() {
return (
<div className="overviewBar">
<div className="currentPrice panel">
{ this.state.currentPrice != null ? <div className="price">{this.state.currentPrice}</div> : <div className="price">Loading...</div> }
</div>
</div>
)
}
}
export default PriceOverview;
Thank you in advance to any help, it's much appreciated.

this.setState ({
currentPrice: currentPrice.bpi.USD.rate
})
Do not put an = in this.setState

Ok First thing, when you're writting code on React the components that hold state are the class base components so ... What I see here is that you're creating two class base components so when you pass down props from your app class component to your PriceOverview wich is another class base component you're essentially doing nothing... Because when your constructor on your PriceOverview get call you're creating a new state on that Component and the previous state ( that's is the one you want to pass down) is being overwritten and that's why you're seem null when you want to display it. So it should work if you just change your PriveOverview component to a function base component ( or a dumb component). So this way when you pass down the state via props, you're displaying the correct state inside of your div. This is how would look like.
import React from 'react';
import './css/PriceOverview.css';
import bitcoinLogo from './assets/bitcoin.svg';
const PriceOverview = (data) => {
return (
<div className="overviewBar">
<div className="currentPrice panel">
//Im calling data here because that's the name you gave it as ref
//No need to use 'this.props' you only use that to pass down props
{data != null ? <div className="price">
{data}</div> : <div className="price">Loading...</div>
}
</div>
</div>
)
}
}
export default PriceOverview;
Whenever you're writing new components start always with function base components if you component is just returning markup in it and you need to pass some data go to his parent component update it (making the api calls there or setting the state there) and pass down the props you want to render via ref. Read the React docs as much as you can, hope this explanation was useful (my apologies in advance if you don't understand quite well 'cause of my grammar I've to work on that)

The thing is constructor of any JS class is called only once. It is the render method that is called whenever you call this.setState.
So basically you are setting currentPrice to null for once and all in constructor and then accessing it using state so it will always be null.
Better approch would be using props.
You can do something like this in your PriceOverview.js.
import React, { Component } from 'react';
import './css/PriceOverview.css';
import bitcoinLogo from './assets/bitcoin.svg';
class PriceOverview extends Component {
constructor(props) {
super(props);
this.state = {
}
}
render() {
return (
<div className="overviewBar">
<div className="currentPrice panel">
{ this.props.data!= null ? <div className="price">{this.props.data}</div> : <div className="price">Loading...</div> }
</div>
</div>
)
}
}
export default PriceOverview;
Or you can use react lifecycle method componentWillReceiveProps to update the state of PriceOverview.js
componentWillReceiveProps(nextProps) {
this.setState({
currentPrice:nextProps.data
});
}
render() {
return (
<div className="overviewBar">
<div className="currentPrice panel">
{ this.state.currentPrice != null ? <div className="price">{this.state.currentPrice }</div> : <div className="price">Loading...</div> }
</div>
</div>
)
}
}

React Higher Order Component conditional data load

Imagine I have some "page" component, which needs to ask for data from a server. The data it requests will depend on whether or not the current user is authenticated. Further, in the event of a login, the page will want to reload the data. My question is, how can I accomplish something like this using HOCs rather than inheritance?
To illustrate the problem, I'll demonstrate a solution using inheritance. The program will have the following objects. I'll leave out the boilerplate code.
session: an EventEmitter that emits start when the session changes (either a login or a log out).
Page: the superclass that all pages inherit from
MyPage: the subclass of Page in this example
API: will be an API class for retrieving data from the server
Here's the code:
// Page superclass
class Page extends React.Component {
componentWillMount() {
session.on("start", this.loadData);
this.loadData();
}
loadData() {
// this method is overwritten in subclasses
}
}
// MyPage subclass
class MyPage extends Page {
loadData() {
if(session.isAuthenticated()) {
API.loadPrivateData();
} else {
API.loadPublicData();
}
}
}
Here's a solution that uses an HOC, but seems less elegant than inheritance. It still requires that every "subclass" page have a method loadData, and it requires that method to be called in every "subclass's" componentWillMount.
// Page HOC
function Page(WrappedComponent) {
return class EnhancedPage extends React.Component {
componentWillMount() {
session.on("start", this.loadData);
// this._page.loadData() will fail here
// since this._page is undefined until rendering finishes
}
loadData() {
this._page.loadData();
}
render() {
return <WrappedComponent {...props} ref={(e) => { this._page = e; }} />
}
}
}
// MyPage
class MyPage extends React.Component {
componentWillMount() {
this.loadData();
}
loadData() {
if(session.isAuthenticated()) {
API.loadPrivateData();
} else {
API.loadPublicData();
}
}
}
const component = Page(MyPage)
// what would make sense here is to have a method something like
// const component = Page(MyPage, () => MyPage.loadData())
// but then the MyPage.loadData logic would need to be defined
// elsewhere
This pattern will happen often: I'll want to load some data, then reload when the session changes. I'd like to understand the "react" way of accomplishing the same.
EDIT: I am not trying to pass a username or "loggedIn" flag through the HOC. That is to say something like <WrappedComponent isLoggedIn={session.isAuthenticated()} {...props} /> won't cut it here. Tying the API logic to props requires that I check for changes in MyPage.componentWillUpdate().

When using a HOC you shouldn't place the loadData function on the wrapped component. Instead pass the function as a parameter to the HOC constructor.
Something like this might work for you. The sessionHoc function takes a callback function which'll be called every time the session state changes. Its result will be passed to WrappedComponent as a data prop.
function sessionHoc(onSessionChange) {
return function (WrappedComponent) {
return class extends React.Component {
constructor(props) {
super(props);
this.state = {
data: null,
};
session.on('start', this.handleSessionChange.bind(this));
}
handleSessionChange() {
this.setState({
data: onSessionChange(),
});
}
render() {
return <WrappedComponent data={data} {...this.props} />
}
};
};
}
class MyPage extends React.Component {
render() {
// Just access this.props.data here!
}
}
const EnhancedPage = sessionHoc(function () {
if (session.isAuthenticated()) {
return API.loadPrivateData();
} else {
return API.loadPublicData();
}
})(MyPage);
Hopefully this helped! :)