REACT

Aditi Dosi
3 min readAug 30, 2022
React is a free and open-source front-end JavaScript library for building user interfaces based on UI components. It is maintained by Meta and a community of individual developers and companies.

A Simple Component

React components implement a render() method that takes input data and returns what to display. This example uses an XML-like syntax called JSX. Input data that is passed into the component can be accessed by render() via this.props.

JSX is optional and not required to use React. Try the Babel REPL to see the raw JavaScript code produced by the JSX compilation step.

JSX EDITOR

class HelloMessage extends React.Component {
render() {
return <div>Hello {this.props.name}</div>;
}
}root.render(<HelloMessage name="Taylor" />);

RESULT

Hello Taylor

Declarative

React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes.

Declarative views make your code more predictable and easier to debug.

Component-Based

Build encapsulated components that manage their own state, then compose them to make complex UIs.

Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep state out of the DOM.

Learn Once, Write Anywhere

We don’t make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code.

React can also render on the server using Node and power mobile apps using React Native.

A Stateful Component

In addition to taking input data (accessed via this.props), a component can maintain internal state data (accessed via this.state). When a component’s state data changes, the rendered markup will be updated by re-invoking render().

JSX EDITOR

class Timer extends React.Component {
constructor(props) {
super(props);
this.state = { seconds: 0 };
}

tick() {
this.setState(state => ({
seconds: state.seconds + 1
}));
}

componentDidMount() {
this.interval = setInterval(() => this.tick(), 1000);
}

componentWillUnmount() {
clearInterval(this.interval);
}

render() {
return (
<div>
Seconds: {this.state.seconds}
</div>
);
}
}

root.render(<Timer />);

RESULT

Seconds: 194

An Application

Using props and state, we can put together a small Todo application. This example uses state to track the current list of items as well as the text that the user has entered. Although event handlers appear to be rendered inline, they will be collected and implemented using event delegation.

JSX EDITOR

class TodoApp extends React.Component {
constructor(props) {
super(props);
this.state = { items: [], text: '' };
this.handleChange = this.handleChange.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
}

render() {
return (
<div>
<h3>TODO</h3>
<TodoList items={this.state.items} />
<form onSubmit={this.handleSubmit}>
<label htmlFor="new-todo">
What needs to be done?
</label>
<input
id="new-todo"
onChange={this.handleChange}
value={this.state.text}
/>
<button>
Add #{this.state.items.length + 1}
</button>
</form>
</div>
);
}

handleChange(e) {
this.setState({ text: e.target.value });
}

handleSubmit(e) {
e.preventDefault();
if (this.state.text.length === 0) {
return;
}
const newItem = {
text: this.state.text,
id: Date.now()
};
this.setState(state => ({
items: state.items.concat(newItem),
text: ''
}));
}
}

class TodoList extends React.Component {
render() {
return (
<ul>
{this.props.items.map(item => (
<li key={item.id}>{item.text}</li>
))}
</ul>
);
}
}

root.render(<TodoApp />);

RESULT

TODO

What needs to be done?

Add #1

A Component Using External Plugins

React allows you to interface with other libraries and frameworks. This example uses remarkable, an external Markdown library, to convert the <textarea>’s value in real time.

JSX EDITOR

class MarkdownEditor extends React.Component {
constructor(props) {
super(props);
this.md = new Remarkable();
this.handleChange = this.handleChange.bind(this);
this.state = { value: 'Hello, **world**!' };
}

handleChange(e) {
this.setState({ value: e.target.value });
}

getRawMarkup() {
return { __html: this.md.render(this.state.value) };
}

render() {
return (
<div className="MarkdownEditor">
<h3>Input</h3>
<label htmlFor="markdown-content">
Enter some markdown
</label>
<textarea
id="markdown-content"
onChange={this.handleChange}
defaultValue={this.state.value}
/>
<h3>Output</h3>
<div
className="content"
dangerouslySetInnerHTML={this.getRawMarkup()}
/>
</div>
);
}
}

root.render(<MarkdownEditor />);

RESULT

Input

Enter some markdown

Output

Hello, world!

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