Develop Reference

Inserting a element into REACT child

I am rendering a chart with react, and I would like to add an element to the title of that chart. Unfortunately, I am using a shared chart component, and majorly modifying the component would be difficult to justify.
I have tried using refs; however, I'm running into difficulty figuring how to actually append a virtual dom element as a child element.
Specific Chart Class:
class ChartWithInfo extends React.Component {
constructor(props){
super(props);
this.chartWrapperElement = React.createRef();
}
componentDidMount() {
const infoInsertion = (
<div>
<IconButton/>
</div>
)
this.chartWrapperElement.current.insertBefore(infoInsertion, this.chartWrapperElement.current.firstChild);
}
render() {
return (
<GenericChart
variables={this.props.variables}
ref={this.chartWrapperElement}
/>
);
}
}
Generic Chart Class
export default class EmbeddedChart extends PureComponent {
// Random methods //
render() {
return (
<div ref={this.props.ref} id={'chartDiv'}>
Chart
</div>
);
}
}
The expected result would essentially be:
<div id='chartDiv'>
<IconButton/>
</div>
What is the most react way to do this? Am I missing something with refs?

React is meant for components and if you follow the separation of concern and component architecture. You can segregate all your components and individual reusable components. Create your button component separately and import anywhere else. Bind your events and business logic respectively.

How can I prevent my functional component from re-rendering with React memo or React hooks?

When hiddenLogo changes value, the component is re-rendered. I want this component to never re-render, even if its props change. With a class component I could do this by implementing sCU like so:
shouldComponentUpdate() {
return false;
}
But is there a way to do with with React hooks/React memo?
Here's what my component looks like:
import React, { useEffect } from 'react';
import PropTypes from 'prop-types';
import ConnectedSpringLogo from '../../containers/ConnectedSpringLogo';
import { Wrapper, InnerWrapper } from './styles';
import TitleBar from '../../components/TitleBar';
const propTypes = {
showLogo: PropTypes.func.isRequired,
hideLogo: PropTypes.func.isRequired,
hiddenLogo: PropTypes.bool.isRequired
};
const Splash = ({ showLogo, hideLogo, hiddenLogo }) => {
useEffect(() => {
if (hiddenLogo) {
console.log('Logo has been hidden');
}
else {
showLogo();
setTimeout(() => {
hideLogo();
}, 5000);
}
}, [hiddenLogo]);
return (
<Wrapper>
<TitleBar />
<InnerWrapper>
<ConnectedSpringLogo size="100" />
</InnerWrapper>
</Wrapper>
);
};
Splash.propTypes = propTypes;
export default Splash;

As G.aziz said, React.memo functions similarly to pure component. However, you can also adjust its behavior by passing it a function which defines what counts as equal. Basically, this function is shouldComponentUpdate, except you return true if you want it to not render.
const areEqual = (prevProps, nextProps) => true;
const MyComponent = React.memo(props => {
return /*whatever jsx you like */
}, areEqual);

React.memo is same thing as React.PureComponent
You can use it when you don't want to update a component that you think is static so, Same thing as PureCompoment.
For class Components:
class MyComponents extends React.PureCompoment {}
For function Components:
const Mycomponents = React.memo(props => {
return <div> No updates on this component when rendering </div>;
});
So it's just creating a component with React.memo
To verify that your component doesn't render you can just
activate HightlightUpdates in react extension and check your components reaction on
rendering

We can use memo for prevent render in function components for optimization goal only. According React document:
This method only exists as a performance optimization. Do not rely on it to “prevent” a render, as this can lead to bugs.

According to react documentation:- [https://reactjs.org/docs/react-api.html][1]
React. memo is a higher order component. If your component renders the
same result given the same props, you can wrap it in a call to React.
memo for a performance boost in some cases by memoizing the result.
This means that React will skip rendering the component, and reuse the
last rendered result.
For practical understanding I came across these two videos they are very good if you wanna clear concepts also, better to watch so it'll save your time.
Disclaimer:- This is not my YouTube channel.
https://youtu.be/qySZIzZvZOY [ useMemo hook]
https://youtu.be/7TaBhrnPH78 [class based component]

Use ref in Higher Order Components

I have a Table component that I want ref to be attached to.
Use: Table.js
class Table extends React.Component {
constructor(props) {
super(props);
this.state = {
rows: 1,
dataLength: props.dataLength,
}
this.tableRef = React.createRef();
}
componentDidUpdate() {
//using ref
this.tableRef.current ..... //logic using ref
this.state.rows ..... //some logic
}
render() {
<TableContainer ref={this.tableRef} />
<CustomPagination />
}
}
This works fine, but now my requirement has changed, and I want to reuse the Table component with pagination applied to all the Tables in my App. I have decided to make a HOC withCustomPagination.
Use: withCustomPagination.js HOC
import CustomPagination from 'path/to/file';
const withCustomPagination = tableRef => Component => {
return class WithCustomPagination extends React.Component {
constructor(props) {
super(props);
this.state = {
rows: 1,
dataLength: props.dataLength,
}
}
componentDidUpdate() {
tableRef.current.state ..... //logic using ref, Error for this line
this.state.rows ..... //some logic
}
render() {
return (
<Component {...state} />
<CustomPagination />
)
}
}
}
export default withCustomPagination;
New Table.js:
import withCustomPagination from '/path/to/file';
const ref = React.createRef();
const Table = props => (
<TableContainer ref={ref} />
);
const WrappedTable = withCustomPagination(ref)(Table);
HOC withCustomPagination returns a class WithCustomPagination that has a componentDidUpdate lifecycle method that uses Table ref in the logic. So I try to pass ref created in Table.js as argument to withCustomPagination, i.e curried with ref and Table stateless component.
This use of ref is wrong and I get error: TypeError: Cannot read property 'state' of null.
I tried using Forwarding Refs, but was unable to implement it.
How do I pass the Table ref to withCustomPagination and be able to use it in HOC?

In this case you can use useImperativeHandle
It means you have to forward ref and specify which function or object or,...
you want to share with ref inside your functional component.
Here is my Hoc example :
import React from 'react';
import { View } from 'react-native';
export function CommonHoc(WrappedComponent) {
const component = class extends React.Component {
componentDidMount() {
this.refs.myComponent.showAlert();
}
render() {
return (
<>
<WrappedComponent
ref='myComponent'
{...this.state}
{...this.props}
/>
</>
);
}
};
return component;
}
and it's my stateless component
const HomeController=(props,ref)=> {
useImperativeHandle(ref, () => ({
showAlert() {
alert("called");
},
}));
return (
<Text>home</Text>
);
};
export default CommonHoc(forwardRef(HomeController));

Either restructure your code to not use a HOC for this or try using React.forwardRef:
Refs Aren’t Passed Through
While the convention for higher-order components is to pass through
all props to the wrapped component, this does not work for refs.
That’s because ref is not really a prop — like key, it’s handled
specially by React. If you add a ref to an element whose component is
the result of a HOC, the ref refers to an instance of the outermost
container component, not the wrapped component.
The solution for this problem is to use the React.forwardRef API
(introduced with React 16.3). Learn more about it in the forwarding
refs section.
via Higher-Order Components: Refs Aren’t Passed Through
In the forwarding refs section there are code examples you could use to pass refs down, but trying to yank them up will fail in your case with:
Warning: Stateless function components cannot be given refs. Attempts to access this ref will fail.
In a project we took a different approach. There's an EnhancedTable component that handles all of the pagination logic and in itself has the dumb table component and the pagination component. It works pretty well but this means you would have to drill props (or use a store lib like Redux or Mobx) and add new ones that will handle pagination options. This will result in some refactoring of Table uses and you'll have to be more explicit but I would take it as a boon rather than a hindrance.

I was able to solve a simmilar issue that brought me to this thread without using forwardRef or useImperativeHandle.
By creating the ref at a higher level, and passign it down into the component and sub components that I needed to act on with the ref.
/** Parent Component has access to ref and functions that act on ref **/
import { useRef } from 'react';
const formRef = useRef(); // ref will have dom elements need accessing
const onClickFunction=()=>{ //sample function acts on ref
var inputs = formRef.current.querySelectorAll('input')
/* Act on ref here via onClick function, etc has access to dom elements
in child component and childs child components */
};
return(
<ComponentGetsAttachedRef formRef={formRef} />
//^ref sent down to component and its children
<ComponentNeedingRef onClickFunction={onClickFunction}/>
//^function with access to ref sent down to component
)
/** Child component needs to act on ref**/
export const ComponentNeedingRef = ({ onClickFunction}) =>{
return(
<button onClick={onClickFunction}>
)
}
/* Child component recieves ref and passes it down */
export const ComponentGetsAttachedRef = ({ formRef}) =>{
//ref comes in as prop gets attached to props or utilized internally
return (
<ChildsChildComponent formRef={formRef}/> //sub component passed ref down
)
}

Passing props to children not working In React

This should be super simple for some of you. I have a super simple app that I am making to teach myself the glory that is React and reactDom. Currently, I am pulling from an API (which actually works!), however, I am unable to see any data when rendering to the screen. Literally just two components. I am sure that I am using props or state wrong here, I just don't know where. It's possible that my map function is the problem as well.
Here is the code:
Parent:
import React from "react";
import ReactDOM from "react-dom";
import axios from 'axios'
import { Table } from './Table'
export class DataList extends React.Component {
state = {
articles: []
}
componentDidMount() {
axios.get('http://127.0.0.1:8000/api/portblog/')
.then(res => {
this.setState({
articles: res.data
})
console.log(res.data)
})
}
render() {
return(
<div>
<Table id={this.state.articles.id} articles={this.state.articles} />
</div>
)
}
}
export default DataList
And the child:
import React from "react";
import PropTypes from "prop-types";
import key from "weak-key";
export const Table = (props) => (
<div>
<h1>Welcome to the Article List Page Home</h1>
<li>{props.articles.map((article) => {
{article.titles}
})}</li>
</div>
);
export default Table;

The problem is that your map() call is not returning anything. You need to do something like:
<div>
<h1>Welcome to the Article List Page Home</h1>
{props.articles.map(article =>
<li>{article.titles}</li>
)}
</div>
I'm not exactly sure what your desired output is, but generally you map over data to generate a set of dom elements.

The problem is
<li>{props.articles.map((article) => {
{article.titles}
})}</li>
JSX expressions cannot be used in any arbitrary place. props.articles.map(...) is already an expression, so creating a new one wouldn't make sense.
{article.titles} inside a function creates a block that does nothing. Nothing is returned from map callback, the array isn't mapped to anything.
Depending on what should resulting layout look like, it should be either
<li>{props.articles.map((article) => article.titles)}</li>
output titles within single <li> tag, or
{props.articles.map((article) => <li>{article.titles}</li>)}
to output a list of <li> tags.
ESLint array-callback-return rule can be used to prevent the problem with callback return value.

Understanding React Higher-Order Components

Can someone please explain Higher-order components in React. I have read and re-read the documentation but cannot seem to get a better understanding. According to the documentation, HOCs help remove duplication by creating a primary function that returns a react component, by passing arguments to that function.
I have a few questions on that.
If HOCs create a new enhanced component, can it be possible not to pass in any component as argument at all?
In an example such as this, which is the higher order component, the Button or the EnhancedButton.
I tried creating one HOC like this:
// createSetup.js
import React from 'react';
export default function createSetup(options) {
return class extends React.Component {
constructor(props) {
super(props);
this.state = {};
this.testFunction = this.testFunction.bind(this);
}
testFunction() {
console.log("This is a test function");
}
render() {
return <p>{options.name}</p>
}
}
}
// main.js
import React from 'react';
import {render} from 'react-dom';
import createSetup from './createSetup';
render((<div>{() => createSetup({name: 'name'})}</div>),
document.getElementById('root'););
Running this does not show the HOC, only the div
Can anyone help out with a better example than the ones given?

A HOC is a function that takes a Component as one of its parameters and enhances that component in some way.
If HOCs create a new enhanced component, can it be possible not to pass in any component as argument at all?
Nope, then it wouldn't be a HOC, because one of the conditions is that they take a component as one of the arguments and they return a new Component that has some added functionality.
In an example such as this, which is the higher order component, the Button or the EnhancedButton.
EnhanceButton is the HOC and FinalButton is the enhanced component.
I tried creating one HOC like this: ... Running this does not show the HOC, only the div
That's because your createSetup function is not a HOC... It's a function that returns a component, yes, but it does not take a component as an argument in order to enhance it.
Let's see an example of a basic HOC:
const renderWhen = (condition, Component) =>
props => condition(props)
? <Component {...props} />
: null
);
And you could use it like this:
const EnhancedLink = renderWhen(({invisible}) => !invisible, 'a');
Now your EnhancedLink will be like a a component but if you pass the property invisible set to true it won't render... So we have enhanced the default behaviour of the a component and you could do that with any other component.
In many cases HOC functions are curried and the Component arg goes last... Like this:
const renderWhen = condition => Component =>
props => condition(props)
? <Component {...props} />
: null
);
Like the connect function of react-redux... That makes composition easier. Have a look at recompose.

In short, If you assume functions are analogues to Components, Closure is analogous to HOC.

Try your createSetup.js with:
const createSetup = options => <p>{options.name}</p>;
and your main.js
const comp = createSetup({ name: 'name' });
render((<div>{comp}</div>),
document.getElementById('root'));

A higher-order component (HOC) is an advanced technique in React for reusing component logic. Concretely, a higher-order component is a function that takes a component and returns a new component.
A HOC is a pure function with zero side-effects.
Example: CONDITIONALLY RENDER COMPONENTS
Suppose we have a component that needs to be rendered only when a user is authenticated — it is a protected component. We can create a HOC named WithAuth() to wrap that protected component, and then do a check in the HOC that will render only that particular component if the user has been authenticated.
A basic withAuth() HOC, according to the example above, can be written as follows:
// withAuth.js
import React from "react";
export function withAuth(Component) {
return class AuthenticatedComponent extends React.Component {
isAuthenticated() {
return this.props.isAuthenticated;
}
/**
* Render
*/
render() {
const loginErrorMessage = (
<div>
Please login in order to view this part of the application.
</div>
);
return (
<div>
{ this.isAuthenticated === true ? <Component {...this.props} /> : loginErrorMessage }
</div>
);
}
};
}
export default withAuth;
The code above is a HOC named withAuth. It basically takes a component and returns a new component, named AuthenticatedComponent, that checks whether the user is authenticated. If the user is not authenticated, it returns the loginErrorMessage component; if the user is authenticated, it returns the wrapped component.
Note: this.props.isAuthenticated has to be set from your application’s
logic. (Or else use react-redux to retrieve it from the global state.)
To make use of our HOC in a protected component, we’d use it like so:
// MyProtectedComponent.js
import React from "react";
import {withAuth} from "./withAuth.js";
export class MyProectedComponent extends React.Component {
/**
* Render
*/
render() {
return (
<div>
This is only viewable by authenticated users.
</div>
);
}
}
// Now wrap MyPrivateComponent with the requireAuthentication function
export default withAuth(MyPrivateComponent);
Here, we create a component that is viewable only by users who are authenticated. We wrap that component in our withAuth HOC to protect the component from users who are not authenticated.
Source

// HIGHER ORDER COMPOENTS IN REACT
// Higher order components are JavaScript functions used for adding
// additional functionalities to the existing component.
// file 1: hoc.js (will write our higher order component logic) -- code start -->
const messageCheckHOC = (OriginalComponent) => {
// OriginalComponent is component passed to HOC
const NewComponent = (props) => {
// business logic of HOC
if (!props.isAllowedToView) {
return <b> Not Allowed To View The MSG </b>;
}
// here we can pass the props to component
return <OriginalComponent {...props} />;
};
// returning new Component with updated Props and UI
return NewComponent;
};
export default messageCheckHOC;
// file 1: hoc.js -- code end -->
// file 2: message.js -- code start -->
// this is the basic component we are wrapping with HOC
// to check the permission isAllowedToView msg if not display fallback UI
import messageCheckHOC from "./hoc";
const MSG = ({ name, msg }) => {
return (
<h3>
{name} - {msg}
</h3>
);
};
export default messageCheckHOC(MSG);
// file 2: message.js -- code end -->
// file 3 : App.js -- code start --->
import MSG from "./message.js";
export default function App() {
return (
<div className="App">
<h3>HOC COMPONENTS </h3>
<MSG name="Mac" msg="Heyy !!! " isAllowedToView={true} />
<MSG name="Robin" msg="Hello ! " isAllowedToView={true} />
<MSG name="Eyann" msg="How are you" isAllowedToView={false} />
</div>
);
}
// file 3 : App.js -- code end --->