The "React Certificate" likely refers to a certification demonstrating proficiency in React, a popular JavaScript library used for building user interfaces, particularly single-page applications. It's maintained by Facebook and a community of individual developers and companies.
React allows developers to build web applications that can update and render efficiently in response to data changes. It introduces the concept of the component, a reusable piece of UI that can be nested, managed, and handled independently.
React components are JavaScript functions or classes that return a React element. Components can receive inputs called "props" to render UI.
function Welcome(props) {
return Hello, {props.name};
}
To render the `Welcome` component:
<Welcome name="Sarah" />
State is a feature available to class components (and functional components using the `useState` hook) in React. It allows components to maintain internal data that can change over time.
class Timer extends React.Component {
constructor(props) {
super(props);
this.state = { seconds: 0 };
}
componentDidMount() {
this.interval = setInterval(() => this.tick(), 1000);
}
componentWillUnmount() {
clearInterval(this.interval);
}
tick() {
this.setState(state => ({
seconds: state.seconds + 1
}));
}
render() {
return (
<div>
Seconds: {this.state.seconds}
</div>
);
}
}
Hooks are functions that let developers "hook into" React state and lifecycle features from function components. The most common hooks are `useState` and `useEffect`.
import React, { useState, useEffect } from 'react';
function Timer() {
const [seconds, setSeconds] = useState(0);
useEffect(() => {
const interval = setInterval(() => {
setSeconds(seconds => seconds + 1);
}, 1000);
return () => clearInterval(interval);
}, []);
return <div>Seconds: {seconds}</div>;
}
The Context API is a component structure provided by React to share values like themes and authentication status between components.
const ThemeContext = React.createContext('light');
class App extends React.Component {
render() {
return (
<ThemeContext.Provider value="dark">
<Toolbar />
</ThemeContext.Provider>
);
}
}
function Toolbar() {
return (
<div>
<ThemedButton />
</div>
);
}
class ThemedButton extends React.Component {
static contextType = ThemeContext;
render() {
return <Button theme={this.context} />;
}
}
Redux is a predictable state container for JavaScript apps, and it’s commonly used with React.
import { createStore } from 'redux';
function counterReducer(state = 0, action) {
switch (action.type) {
case 'INCREMENT':
return state + 1;
default:
return state;
}
}
const store = createStore(counterReducer);
store.subscribe(() => console.log(store.getState()));
store.dispatch({ type: 'INCREMENT' });
React Router is a standard library for routing in React that enables the navigation among views in a Single Page Application, ensuring that the user interface synchronizes with the URL.
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
function App() {
return (
<Router>
<Switch>
<Route path="/about">
<About />
</Route>
<Route path="/">
<Home />
</Route>
</Switch>
</Router>
);
}
React provides a set of utilities to test components in isolation and simulate user interaction. The most commonly used testing libraries are Jest and React Testing Library.
import { render, screen } from '@testing-library/react';
import '@testing-library/jest-dom';
import MyComponent from './MyComponent';
test('renders learn react link', () => {
render(<MyComponent />);
const linkElement = screen.getByText(/learn react/i);
expect(linkElement).toBeInTheDocument();
});
Managing side effects like data fetching, subscriptions, or manual DOM manipulations in functional components can be handled by the `useEffect` Hook.
import React, { useEffect, useState } from 'react';
function Example() {
const [data, setData] = useState(null);
useEffect(() => {
fetch('https://api.example.com/data')
.then((response) => response.json())
.then((data) => setData(data));
}, []);
return <div>{data ? data.title : 'Loading...'}</div>;
}
React.lazy helps in loading components lazily through code splitting. Suspense lets your components “wait” for something before rendering.
const OtherComponent = React.lazy(() => import('./OtherComponent'));
function MyComponent() {
return (
<div>
<React.Suspense fallback={<div>Loading...</div>}>
<OtherComponent />
</React.Suspense>
</div>
);
}
Higher-Order Components (HOCs) are a way to reuse component logic. HOCs are not part of the React API but are a pattern emerging from React’s compositional nature.
function withSubscription(WrappedComponent, selectData) {
return class extends React.Component {
constructor(props) {
super(props);
this.state = {
data: selectData(DataSource, props)
};
}
render() {
return <WrappedComponent data={this.state.data} {...this.props} />;
}
};
}
To practically apply React knowledge, one could start by building a simple project, for example, a to-do list application. Create different components, manage states, props, and apply styles to get hands-on experience in React development.
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