This question already has answers here:
componentDidMount equivalent on a React function/Hooks component?
(11 answers)
Closed 3 months ago.
I have a function which is technically a React Functional Component:
export default function Daw() {
return (
<>
<div>Hello world.</div>
</>
);
}
Of course, my ordinary function cannot have the ReactJS method of componentDidMount(). Since it is not a class which extends React.PureComponent.
I'm using this function inside a ReactJS web app.
export default function Daw() {
componentDidMount() { // ** Cannot use this ReactJS method!?
}
return (
<>
<div>Hello world.</div>
</>
);
}
Question
How can I possibly call componentDidMount() method of ReactJS inside my ordinary function? Is there a way to do it, without converting my function to a class which extends React.PureComponent? Is it possible?
First import useEffect from react
import { useEffect } from "react";
Then use useEffect with an empty dependency array,it is same as componentDidMount()
useEffect(() => { console.log("Mounted"); },[]);
Refer react official documentation for learning all lifecycle methods using useEffect hook:- https://reactjs.org/docs/hooks-effect.html
You're going to need React Hooks! All life-cycle methods we were doing in class components are available in functional components too via React Hooks, even in a better way. Read more about React hooks here: https://reactjs.org/docs/hooks-intro.html
And in this case, the equivalent of componentDidMount is this:
import { useEffect } from 'react'
export default function Daw() {
useEffect(() => {
// Code here will run just like componentDidMount
}, [])
return (
<>
<div>Hello world.</div>
</>
)
}
You can also learn about Effects in React by reading my article: A Beginner’s Guide to Effects in React
You cannot use componentDidMount() (class lifecycle methods) in React functional components. Instead you can use useEffect hook to perform the same operation. Like this:
useEffect(() => {
}, []);
Check here for more info - Similar Question
yes, you can use useEffect hook.
useEffect has the following abilities of class methods .i.e. componentDidMount, componentDidUpdate and componentWillUnmoun.
refer following info from official doc:
https://reactjs.org/docs/hooks-effect.html
Related
Here is where I would like to use my hook so that I can change one state during the run of the app.
export const simpleFunction = () => (state) => {
// here is the hook
}
I know react hooks should be used in functional components, but what about the case stated above.
Yes you can! Those functions are then called custom hooks. But it is required to use those custom hooks inside of a functional component. So technically it is now a function using hooks outside of a react component, but they still need to be bound to a component later.
Building your own Hooks lets you extract component logic into reusable functions.
Docs: https://reactjs.org/docs/hooks-custom.html
Example from the docs
import { useState, useEffect } from 'react';
function useFriendStatus(friendID) {
const [isOnline, setIsOnline] = useState(null);
useEffect(() => {
function handleStatusChange(status) {
setIsOnline(status.isOnline);
}
ChatAPI.subscribeToFriendStatus(friendID, handleStatusChange);
return () => {
ChatAPI.unsubscribeFromFriendStatus(friendID, handleStatusChange);
};
});
return isOnline;
}
Because your descriptions is so short I don't know if this is what you are looking for. Hope I could help :)
I have a quite big React component SearchProvider written as a class and a UI component InputRange that I wrote as functional component using Hooks.
ATM I am getting the error "Invalid hook call. Hooks can only be called inside of the body of a function component."
Can I use the hook component as a child of the class component?
import { InputRange } from 'react-components';
class SearchProvider extends Component {
render() {
return <Fragment>
<InputRange />
{this.props.children}
</Fragment>;
}
function InputRange(props) {
...
useEffect(_ => { ...});
return <div className="input-range"></div>;
}
I answer my own question. The problem was duplicated react and not directly related to hooks. See https://reactjs.org/warnings/invalid-hook-call-warning.html#duplicate-react
I had to declare react and react-dom in the UI component as peerDependencies. This solves the problem.
I've created my React class like such:
const MyMap = () => {
componentDidMount() {
...
}
return {
...
}
}
I realized that componentDidMount() is not being recognized and is not working. Is this because I didn't extend React.Component? Also, is there an alternative I can use for the React class I created?
you could use useEffect hook
useEffect(() => {
// write your logic here
}, []);
as they mention here
The Effect Hook, useEffect, adds the ability to perform side effects from a function component. It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in React classes
I am new to React and trying to add the Floating Menu Button from this Package.
Adding this I get following Error.
Parsing error: Unexpected token
I have uploaded the Code.
https://codesandbox.io/s/adding-floatingmenu-2tfxe?file=/src/App.js
I also have another Question. What is the difference of adding render() {} infront of return() or just leaving return()?
Update
I have Updated my Code inside codesandbox, there i do not receive an Error, after I copied it into VSCode i receive following error.
You can use react hooks only in functional components. If you use class components you not allowed to use hooks.
But what is a Hook?
Hooks are functions that let you “hook into” React state and lifecycle features from function components. Hooks don’t work inside classes — they let you use React without classes.
Second question the same situation, render() uses in class components, in functional components you just use return(<></>)
Please read hooks owerview:
https://reactjs.org/docs/hooks-overview.html
If you want to initialize the isOpen state as false, here's a minimal example of that
import React, { Component } from "react";
import {
FloatingMenu,
MainButton,
ChildButton,
} from "react-floating-button-menu";
export default class Login extends Component {
constructor(props) {
super(props)
this.state = {
isOpen: false
}
}
render() {
return (
<FloatingMenu
slideSpeed={500}
direction="up"
spacing={8}
isOpen={this.state.isOpen}
>
<MainButton
backgroundColor="black"
onClick={() => this.setState({ open: !this.state.isOpen })}
size={56}
/>
</FloatingMenu>
);
}
};
Make sure you import Component from 'react' at the top. Render method is required when you're making a React component using a class method which you are using. It's a type of lifecycle method which is invoked when the component needs to update. The return statement only returns the data/JSX elements wherever it is being used.
If you are using functional components, you don't need a render method since they return the react elements themselves
I've been learning more about React.js function components and have started transitioning one of my React.js applications to use them instead of the standard react components. In my react components I had been making AJAX/API call(s) in the componentDidMount() function. Since that function doesn't exist in function components I am unsure where to put them.
I couldn't find the answer on the React.js site, the only page I could find on AJAX and APIs shows making those calls with react standard components in the componentDidMount() function.
This is what React hooks gives us - ways to do side effects in functional components:
https://reactjs.org/docs/hooks-effect.html
from the doc page:
If you’re familiar with React class lifecycle methods, you can think of useEffect Hook as componentDidMount, componentDidUpdate, and componentWillUnmount combined.
for example:
import React, { useState, useEffect } from 'react';
function Example() {
const [count, setCount] = useState(0);
// Similar to componentDidMount and componentDidUpdate:
useEffect(() => {
//do an ajax call here
});
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
You can use react-pure-lifecycle to add lifecycle functions to functional components.
Example:
import React, { Component } from 'react';
import lifecycle from 'react-pure-lifecycle';
const methods = {
componentDidMount(props) {
//ajax call here
}
};
const Channels = props => (
<h1>Hello</h1>
)
export default lifecycle(methods)(Channels);