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React refs most often return undefined or null when we try to access their current properties before the corresponding DOM element is rendered. To fix this, you need to access the ref in the useEffect hook or when an event is triggered. import {useRef...

To pass a boolean value as props to a component in React, wrap the boolean value in curly braces, e.g. Child bool={true} / . All non-string props that we pass to a component must be enclosed in curly braces. function Child ( {bo...

To get the height of an element using ref in React: Initialize a state variable that will store the element's height. Update the element's height in the useEffect() hook. The height should be set to ref.current.clientHeight . import {useEffect, useSta...

To change the style of an element using ref in React: Set the ref attribute on the element. Access the element through the current attribute on the ref. Update the element's style, for example ref.current.style.backgroundColor = green . import { useRe...

Use square bracket notation to set and access state in React using dynamic keys, for example, setEmployee({...employee, [key]: employee.salary + 100}) . The variable or expression in the square brackets will be evaluated before setting the state. impo...

Add an event listener to the body element: Access the body element on the document object. Use the addEventListener() method on the body element in the useEffect hook. Remove the event listener when the component unmounts. import {useEffect} from reac...

To check if an element is in the Viewport in React.js: Set a ref attribute on the element. Use the IntersectionObserver API to track if elements intersect. App.js import {useEffect, useRef, useState, useMemo} from react ; export default function...

To get the value of an input when the Enter key is pressed in React: Set the onKeyDown property on the input field. When the user presses a key, check if that key is Enter. Access the value of the input field from a state variable. import { useState }...

To clear a timeout or interval in React using hooks: Use the useEffect hook to set a timeout or interval. Return a function from the useEffect hook. Use the clearTimeout() or clearInterval() method to remove the timeout when the component unmounts. , ...

To check if a prop was passed to a component in React: Compare the prop to undefined. If the prop is equal to undefined, then it was not passed to the component. Otherwise, it was passed to the component. const Button = ({withIcon}) = { if...

When two or more elements returned from the map() method have the same key property, a React error Encountered two children with the same key will occur. To fix this error, you need to provide a unique value for the key prop of each element or use ind...

We can export multiple components in React using named exports, such as export function A() {} and export function B() {} . We can import the exported components using named imports, such as import {A, B} from ./another-file . We can use the same name...

When we pass a value that is not a function to the onClick attribute of an element, we get the error Expected onClick listener to be a function . To fix the error, make sure you only pass a function to the onClick attribute of an element. const App = ...

Passing functions as props in React TypeScript: Define the type of the function property in the component's interface. Define the function in the parent component. Pass the function as a prop to the child component. interface ButtonProps { sum : ( a: ...

To create an input field that contains only allowed numbers using React.js: Set the input field's type to text. Add an onChange event handler that removes all non-numeric values. Save the input value in a state variable. import {useSt...