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Calling function defined within a react function component on a click event form another function component - React.js

I am constructing some node objects in a function(prepareNodes) to pass to React Flow within a functional component A (lets say), and I have defined a custom node component(CardNode) stateless, which has a button. On button click it should trigger the function(prepareNodes) defined within Component A.
function ComponentA = ({ selectedNodes }) => {
const reactFlowWrapper = useRef(null);
const [elements, setElements] = useState([]);
const [edges, setEdges] = useState([]);
const prepareNode = async (nodeid) => {
//some service calls to fetch data and constuct nodes
setElements([ ...nodes]);
setEdges([...edges]);
}
return (
<ReactFlowProvider>
<div className="reactflow-wrapper" ref={reactFlowWrapper}>
<ReactFlow
nodes={elements}
edges={edges}
//some properties
>
</ReactFlow>
</div>
</ReactFlowProvider>
)
};
export default ComponentA;
function CardNode({ data }) {
const renderSubFlowNodes = (id) => {
console.log(id);
//prepareNode(id)
}
return (
<>
<Handle type="target" position={Position.Top} />
<div className="flex node-wrapper">
<button className="btn-transparent btn-toggle-node" href="#" onClick={() => renderSubFlowNodes(data['id']) }>
<div>
<img src={Icon}/>
</div>
</button>
</div>
<Handle type="source" position={Position.Bottom}/>
</>
);
}
export default CardNode;
I looked for some references online, and most of them suggest to move this resuable function out of the component, but since this function carries a state that it directly sets to the ReactFlow using useState hook, I dont think it would be much of a help.
Other references talks about using useCallback or useRefs and forwardRef, useImperativeHandle especially for functional component, Which I did not quite understand well.
Can someone suggest me a solution or a work around for this specific use-case of mine.

You can add an onClick handler to the each node, and within the node view you call this handler on click.
In the parent Component within the onClick handler you can call prepareNode as needed.
useEffect(() => {
setElements(
elements.map(item => {
...item,
onClick: (i) => {
console.log(i);
prepareNode();
},
})
)},
[]);

The classical approach is to have a parent object that defines prepareNode (along with the state items it uses) and pass the required pieces as props into the components that use them.
That "parent object" could be a common-ancestor component, or a Context (if the chain from the parent to the children makes it cumbersome to pass the props all the way down it).

How to pass data from vanilla JavaScript to React functional component

I'm trying to update (setState) a React functional component from within "regular" (vanilla) JavaScript.
I searched through StackOverflow but all the answers deal with passing data from React to (vanilla) JavaScript, and not the other way around.
Let's take the example from the docs:
import React, { useState } from 'react';
function Example() {
// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
To render it in JavaScript, I do:
let example = ReactDOM.render(
<Example />,
document.getElementById('example-wrapper')
);
Now suppose I want to manually update the count from the vanilla JavaScript code, outside of react. Like:
function updateExampleCount(newCount) {
example.setCount(newCount); // ???
}
I can't access the component state, as setCount is a private variable inside the function, and example returned from render is null.
If I use a class component, then render returns a reference to the component and then I can call example.setState. But I prefer not to convert my component into a class if I can avoid it.
The docs for render say:
Render a React element into the DOM in the supplied container and return a reference to the component (or returns null for stateless components).
But my component does have a state (count), it just doesn't recognize it.
If it's not possible to use the return value from render, is there another way to "get" the component and then use setCount (or some other way to set the state)?
Or do I just have to use a class component for this?
Thanks.

There is no way to access the state from outside the component. It's like trying to access a locally scoped variable from outside a function.
Using a class component wouldn't help either since you wouldn't be able to get hold of the instance of the class created inside the React app.
If you want to trigger a state change from outside the application, then the application needs to provide an event handler.
For (a really quick and dirty) example:
const outside = {
value: 2,
callbacks: [],
addCallback: function (callback) { this.callbacks.push(callback); },
setValue: function (value) {
this.value = value;
this.callbacks.forEach(
callback => callback(this.value)
);
}
};
function Component = () => {
const [val, setVal] = useState(outside.value);
useEffect(() => {
outside.addCallback((value) => setVal(value));
}, []);
return <p>{val}</p>
}

It is possible. You could pass your setCount function as a parameter to use it in your JS outside of React - but I would not really recommend this.
I would recommend that you keep your business logic and React logic separate.
The only things that need to be aware of state and will be using it are React components themselves. I would structure your code in a way that it is not coupled to React, and does not have to use or depend on React state in any way.
This is easier said than done at the beginning. If you need help with it, maybe provide a use case that you are trying to solve in this way, and a better answer might be provided.

It can be done by extending Example so it will pass a reference to the setCount function back to the parent code, see below. (This might be the same as what Oli mentioned, if so then I had the same idea and made a working implementation before answering)
const { useState } = React;
// functionFromComponent will store the function from Example.
let functionFromComponent = undefined;
const setter = (someFn) => functionFromComponent = someFn;
const Example = ({ setFunction }) => { // take `setFunction` from props
const [count, setCount] = useState(0);
setFunction(setCount); // pass setCount to the parent code
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
ReactDOM.render(
<Example setFunction={setter} />,
document.getElementById('example-wrapper')
);
function buttonClicked() {
if (functionFromComponent) {
functionFromComponent(777);
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/17.0.1/umd/react-dom.production.min.js"></script>
<div id="example-wrapper"></div>
<button id="regularButton" onclick="buttonClicked()">Regular button</button>

Is this a valid way of updating state that depends on prevState?

I am following along with a video tutorial on using React. The presenter is currently detailing how to add a toggle button to a UI. They said to give it a go first before seeing how they do it, so I implemented it myself. My implementation was a little different to theirs, just the handler was different; but it does seem to work.
Can anyone with more experience using React tell me, is my toggleSideDrawerHandler wrong in some way? Or is it a valid shorter way of setting the state that depends on a previous state?
My implementation:
//Layout.js
class Layout extends Component {
state = {
showSideDrawer: false
};
toggleSideDrawerHandler = prevState => {
let newState = !prevState.showSideDrawer;
this.setState({ showSideDrawer: newState });
};
closeSideDrawerHandler = () => {
this.setState({ showSideDrawer: false });
};
render() {
return (
<Fragment>
<Toolbar drawerToggleClicked={this.toggleSideDrawerHandler} />
<SideDrawer
open={this.state.showSideDrawer}
close={this.closeSideDrawerHandler}
/>
<main className={styles.Content}>{this.props.children}</main>
</Fragment>
);
}
}
//Toolbar.js
const toolbar = props => (
<header className={styles.Toolbar}>
<DrawerToggle clicked={props.drawerToggleClicked} />
<div className={styles.Logo}>
<Logo />
</div>
<nav className={styles.DesktopOnly}>
<NavItems />
</nav>
</header>
);
Tutorial implementation:
toggleSideDrawerHandler = () => {
this.setState(prevState => {
return { showSideDrawer: !prevState.showSideDrawer };
});
};

Your solution works, but I guess in the part, where you call the toggleSideDrawerHandler you probably call it like
() => this.toggleSideDrawerHandler(this.state)
right?
If not, can you please paste the rest of your code (especially the calling part) to see where you get the prevState from?
This works, because you pass the old state to the method.
I would personally prefer the tutorials implementation, because it takes care of dependencies and the "user" (the dev using it) doesn't need to know anything about the expected data.
With the second implementation all you need to do is call the function and not think about getting and passing the old state to it.
Update after adding the rest of the code:
I think the reason, why it works is because the default value for your parameter is the one passed by the event by default, which is an event object.
If you use prevState.showSideDrawer you are calling an unknown element on this event object, that will be null.
Now if you use !prevState.showSideDrawer, you are actually defining it as !null (inverted null/false), which will be true.
This is why it probably works.
Maybe try to toggle your code twice, by showing and hiding it again.
Showing it will probably work, but hiding it again will not.
This is why the other code is correct.

You should stick to the tutorial implementation. There is no point in passing component state to the children and then from them back to the parents. Your state should be only in one place (in this case in Layout).
Child components should be only given access to the information they need which in this case is just showSideDrawer.

You are using this:
toggleSideDrawerHandler = prevState => {
let newState = !prevState.showSideDrawer;
this.setState({ showSideDrawer: newState });
};
This is a conventional way to update state in react, where we are defining the function and updating state inside. Though you are using term prevState but it doesn't holds any value of components states. When you call toggleSideDrawerHandler method you have to pass value and prevState will hold that value. The other case as tutorial is using:
toggleSideDrawerHandler = () => {
this.setState(prevState => {
return { showSideDrawer: !prevState.showSideDrawer };
});
};
This is called functional setStae way of updating state. In this function is used in setState methods first argument. So prevState will have a value equal to all the states in the component.Check the example below to understand the difference between two:
// Example stateless functional component
const SFC = props => (
<div>{props.label}</div>
);
// Example class component
class Thingy extends React.Component {
constructor() {
super();
this.state = {
temp: [],
};
}
componentDidMount(){
this.setState({temp: this.state.temp.concat('a')})
this.setState({temp: this.state.temp.concat('b')})
this.setState({temp: this.state.temp.concat('c')})
this.setState({temp: this.state.temp.concat('d')})
this.setState(prevState => ({temp: prevState.temp.concat('e')}))
this.setState(prevState => ({temp: prevState.temp.concat('f')}))
this.setState(prevState => ({temp: prevState.temp.concat('g')}))
}
render() {
const {title} = this.props;
const {temp} = this.state;
return (
<div>
<div>{title}</div>
<SFC label="I'm the SFC inside the Thingy" />
{ temp.map(value => ( <div>Concating {value}</div> )) }
</div>
);
}
}
// Render it
ReactDOM.render(
<Thingy title="I'm the thingy" />,
document.getElementById("react")
);
<div id="react"></div>
<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>
So depending on requirement you will use one of the two ways to update the state.

React: How to do conditional checks from render() method in functional Components?

In my normal React class Components, I have done some checks in the render() method, before returning conditional html rendering. Now, I was using a react functional component, which apparently does not have the render() method... how would I do the conditional checks here? Just Inside normal functions and then return html code from those functions?
e.g Class Component:
render() {
let test;
if (this.state.test ===true) {
test = (
<p>This is a test</p>
)
}
return(
{test}
)
}
in functional components? :
return (
<p >
{checkIcon()} //normal Javascript functions?
</p>
)

As stated by others you can do anything inside a render function, the same things you could do with a class component. You can think of your functional components as the render function of your class ones...
Functional components, by the way, should not contain that much business logic, it'd be better to enhance them with HOCs and function composition.
You might want to have a look at recompose, in which my example takes inspiration from. (change the test attribute and press run code snippet)
// First create a Generic HOC that embedds the branching logic for you.
const branch = (predicate, LeftComponent) => RightComponent => props => (
predicate(props) ? <LeftComponent {...props} /> : <RightComponent {...props} />
);
// Leave your view component the only job of displaying data to the screen. Avoid any control flow.
const Test = () => 'this is a test component';
const Value = ({ value }) => <div>The Value is {value}</div>;
// Create a final component that branches accordingly with the needed check (if props.test is true)
const Component = branch(
props => props.test,
Test
)(Value);
ReactDOM.render(
<Component test={true} value="£100" />,
document.getElementById('container')
);
<script crossorigin src="https://unpkg.com/react#16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#16/umd/react-dom.development.js"></script>
<div id="container"></div>

You can think of functional component as a render method of class component where you can do the exact same thing that you do in render except that you will receive props from the arguments instead of this and similarly you won't have state unless your using hooks. So you would pass test as a prop to the functional component
const MyComponent = ({test}) =>{
let value;
if (test ===true) {
test = (
<p>This is a test</p>
)
}
return(
{value}
)
}

How to handle inputs added by button in React [duplicate]

We should avoid method binding inside render because during re-rendering it will create the new methods instead of using the old one, that will affect the performance.
So for the scenarios like this:
<input onChange = { this._handleChange.bind(this) } ...../>
We can bind _handleChange method either in constructor:
this._handleChange = this._handleChange.bind(this);
Or we can use property initializer syntax:
_handleChange = () => {....}
Now lets consider the case where we want to pass some extra parameter, lets say in a simple todo app, onclick of item i need to delete the item from array, for that i need to pass either the item index or the todo name in each onClick method:
todos.map(el => <div key={el} onClick={this._deleteTodo.bind(this, el)}> {el} </div>)
For now just assume that todo names are unique.
As per DOC:
The problem with this syntax is that a different callback is created
each time the component renders.
Question:
How to avoid this way of binding inside render method or what are the alternatives of this?
Kindly provide any reference or example, thanks.

First: A simple solution will be to create a component for the content inside a map function and pass the values as props and when you call the function from the child component you can pass the value to the function passed down as props.
Parent
deleteTodo = (val) => {
console.log(val)
}
todos.map(el =>
<MyComponent val={el} onClick={this.deleteTodo}/>
)
MyComponent
class MyComponent extends React.Component {
deleteTodo = () => {
this.props.onClick(this.props.val);
}
render() {
return <div onClick={this.deleteTodo}> {this.props.val} </div>
}
}
Sample snippet
class Parent extends React.Component {
_deleteTodo = (val) => {
console.log(val)
}
render() {
var todos = ['a', 'b', 'c'];
return (
<div>{todos.map(el =>
<MyComponent key={el} val={el} onClick={this._deleteTodo}/>
)}</div>
)
}
}
class MyComponent extends React.Component {
_deleteTodo = () => {
console.log('here'); this.props.onClick(this.props.val);
}
render() {
return <div onClick={this._deleteTodo}> {this.props.val} </div>
}
}
ReactDOM.render(<Parent/>, document.getElementById('app'));
<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="app"></div>
EDIT:
Second: The other approach to it would be to use memoize and return a function
constructor() {
super();
this._deleteTodoListener = _.memoize(
this._deleteTodo, (element) => {
return element.hashCode();
}
)
}
_deleteTodo = (element) => {
//delete handling here
}
and using it like
todos.map(el => <div key={el} onClick={this._deleteTodoListener(el)}> {el} </div>)
P.S. However this is not a best solution and will still result in
multiple functions being created but is still an improvement over the
initial case.
Third: However a more appropriate solution to this will be to add an attribute to the topmost div and get the value from event like
_deleteTodo = (e) => {
console.log(e.currentTarget.getAttribute('data-value'));
}
todos.map(el => <div key={el} data-value={el} onClick={this._deleteTodo}> {el} </div>)
However, in this case the attributes are converted to string using toString method and hence and object will be converted to [Object Object] and and array like ["1" , "2", "3"] as "1, 2, 3"

How to avoid this way of binding inside render method or what are the
alternatives of this?
If you care about re-rendering then shouldComponentUpdate and PureComponent are your friends and they will help you optimize rendering.
You have to extract "Child" component from the "Parent" and pass always the same props and implement shouldComponentUpdate or use PureComponent. What we want is a case when we remove a child, other children shouldn't be re-rendered.
Example
import React, { Component, PureComponent } from 'react';
import { render } from 'react-dom';
class Product extends PureComponent {
render() {
const { id, name, onDelete } = this.props;
console.log(`<Product id=${id} /> render()`);
return (
<li>
{id} - {name}
<button onClick={() => onDelete(id)}>Delete</button>
</li>
);
}
}
class App extends Component {
constructor(props) {
super(props);
this.state = {
products: [
{ id: 1, name: 'Foo' },
{ id: 2, name: 'Bar' },
],
};
this.handleDelete = this.handleDelete.bind(this);
}
handleDelete(productId) {
this.setState(prevState => ({
products: prevState.products.filter(product => product.id !== productId),
}));
}
render() {
console.log(`<App /> render()`);
return (
<div>
<h1>Products</h1>
<ul>
{
this.state.products.map(product => (
<Product
key={product.id}
onDelete={this.handleDelete}
{...product}
/>
))
}
</ul>
</div>
);
}
}
render(<App />, document.getElementById('root'));
Demo: https://codesandbox.io/s/99nZGlyZ
Expected behaviour
<App /> render()
<Product id=1... render()
<Product id=2... render()
When we remove <Product id=2 ... only <App /> is re-rendered.
render()
To see those messages in demo, open the dev tools console.
The same technique is used and described in article: React is Slow, React is Fast: Optimizing React Apps in Practice by François Zaninotto.

Documentation encourages to use data-attributes and access them from within evt.target.dataset:
_deleteTodo = (evt) => {
const elementToDelete = evt.target.dataset.el;
this.setState(prevState => ({
todos: prevState.todos.filter(el => el !== elementToDelete)
}))
}
// and from render:
todos.map(
el => <div key={el} data-el={el} onClick={this._deleteTodo}> {el} </div>
)
Also note that this makes sense only when you have performance issues:
Is it OK to use arrow functions in render methods?
Generally speaking, yes, it is OK, and it is often the easiest way to
pass parameters to callback functions.
If you do have performance issues, by all means, optimize!

This answer https://stackoverflow.com/a/45053753/2808062 is definitely exhaustive, but I'd say fighting excessive re-renders instead of just re-creating the tiny callback would bring you more performance improvements. That's normally achieved by implementing a proper shouldComponentUpdate in the child component.
Even if the props are exactly the same, the following code will still re-render children unless they prevent it in their own shouldComponentUpdate (they might inherit it from PureComponent):
handleChildClick = itemId => {}
render() {
return this.props.array.map(itemData => <Child onClick={this.handleChildClick} data={itemData})
}
Proof: https://jsfiddle.net/69z2wepo/92281/.
So, in order to avoid re-renders, the child component has to implement shouldComponentUpdate anyway. Now, the only reasonable implementation is completely ignoring onClick regardless of whether it has changed:
shouldComponentUpdate(nextProps) {
return this.props.array !== nextProps.array;
}