Develop Reference

ReactJS - Disabling a component

I need to disable PostList component in its initial state.
import React from 'react';
import PostList from './PostList';
const App = () => {
return (
<div className="ui container">
<PostList />
</div>
);
};
export default App;
Whats the best way to disable (and grey out) a component? Possible solutions are to pass a value as props and then apply it to a ui element, However please keep in mind that PostList may have inner nested components as well. Please share an example.

Since you mentioned in a comment that instead of hiding it, you want to grey it instead. I would use the disabled state and style the component. Since PostList could be nested, we don't know what the props are since you did not specify them.
Also, I assuming that you are not using styled-components.
import React, { useState } from "react";
import PostList from "./PostList";
const App = () => {
const [disabled, setDisabled] = useState(true);
return (
<div className="ui container">
<PostList
style={{
opacity: disabled ? 0.25 : 1,
pointerEvents: disabled ? "none" : "initial"
}}
/>
</div>
);
};
export default App;

There are 2 different ways I like to do something like this.
One way you can do it is by using state
this.state = {
showList: false
}
and than something like
return (
{this.state.showList && <PostList />}
)
Another option is to pass the showList in state as a prop, so something like
return(
<PostList show = {this.state.showList} />
)
and than in PostList something like
return props.show && (your component here)
You can also use conditional classNames, so if you want that component shown, you can throw a className and style it how you normally would, but if not, just throw a display: none. I usually save doing that for replacing a navbar with a dropdown button on smaller screens, but it is another option

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
)
}

React inline functions rerender issue

I have a component that uses two nested components that are based on render prop pattern. I need to combine props from both of them to be sent to the innermost function.
<Component1>
{(...props1) => (
<Component2>
{(...props2) => <MyComponent {...props1} {...props2} />}
</Component2>
)}
</Component1>
Now, I wanted to refactor the above inline functions into class functions, so as to avoid creating new functions on every render.
First attempt:
render() {
return <Component1>{this._render1}</Component1>;
}
_render1 = (...props1) => <Component2>{this._render2}</Component2>;
_render2 = (...props2) => <MyComponent {...props1} {...props2} />;
But now, in render2, I don't have access to props1, so I did:
render() {
return <Component1>{this._render1}</Component1>;
}
_render1 = (...props1) => <Component2>{this._render2(...props1)}</Component2>;
_render2 = (...props1) => (...props2) => <MyComponent {...props1} {...props2} />;
But here, I am back again to original problem of recreating inline functions on each render (inside _render2).
Please suggest a way to mitigate this problem. How can I best send the combined data down? What am I doing wrong here?

Did you got a chance to take a look on React.Context (https://reactjs.org/docs/context.html)?
You can create something like:
SomeContext.jsx
import React from "react";
export const SomeContext = React.createContext();
index.jsx
<SomeContext.Provider value={this.state.contextState}>
<div>
....
<Component2 />
<MyComponent />
...
</div>
</SomeContext.Provider>
Component2.jsx / MyComponent.jsx
import React from "react";
import { SomeContext } from "./SomeContext";
export default () => (
<SomeContext.Consumer>
your jsx with access to the props from parent.
</SomeContext.Consumer>
);
Hope it helps you.

What is the purpose of spreading props in React Higher Order Components?

I'm trying to understand React's Higher Order Component structure, but all the resources just assume you already understand what the purpose of the spread operator is doing in the higher order component when you write:
BaseComponent {...this.props} {...this.state} . Why is it necessary to spread out the props like that if a component is already being passed in as props?
import React, { Component } from 'react';
const EnhanceComponent = BaseComponent => {
return class EnhancedComponent extends Component {
state = {
name: 'You have been enhanced'
}
render() {
return (
<BaseComponent {...this.props} {...this.state} />
)
}
}
};
export default EnhanceComponent;

The answer is directly explained in the docs:
Convention: Pass Unrelated Props Through to the Wrapped Component HOCs add features to a component. They shouldn’t drastically alter
its contract. It’s expected that the component returned from a HOC has
a similar interface to the wrapped component.
HOCs should pass through props that are unrelated to its specific
concern. Most HOCs contain a render method that looks something like
this:
To understand this you should know what {...this.props} does. In your case
const EnhanceComponent = BaseComponent => {
return class EnhancedComponent extends Component {
state = {
name: 'You have been enhanced'
}
render() {
return (
<BaseComponent {...this.props} {...this.state} />
)
}
}
};
export default EnhanceComponent;
EnhanceComponent HOC does a simple operation of adding a state name to the component currently being rendered, so essentially when you use this HOC, you should be able to pass the props required by your original component directly to it rather than consuming them in the HOC, which is what {...this.props} spread syntax is for. You can read this answer for more details on how ... works
Consider the case of a simple component which is used like
<MyComponent className='wrapper-container' onClick={this.handleClick} />
and defined as
class MyComponent extends React.Component {
render() {
const { className, onClick} = this.props;
...
}
}
Now if you use an HOC over this component like
const EnhancedMyComponent = EnhanceComponent(MyComponent);
You would render it like
<EnhancedMyComponent className='wrapper-container' onClick={this.handleClick} />
and now if you don't write {...this.props} in your HOC, then the MyComponent will no longer have className and onClick as props

For example you have a component and you want to enhance it:
const Message = props => (
<div className={props.type}>
<p>{props.message}</p>
</div>
)
const EnhancedMessage = enhance(Message);
Then you can use enhanced component somewhere in your code:
<EnhancedMessage type="alert" message="Something went wrong" />
If you don't spread props passed to HOC how will Message component know about passed props?

Simple answer :
Spreading props is not mandatory
If you want to keep props of a component, to be there after wrapping, then spread props in wrapper component otherwise don't spread it.

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 --->