The first step to getting familiar with a new language is to write a simple “Hello World” program. **React JS** is an open-source JavaScript library for building user interfaces (usually for single-page applications).


# Code

In the code below, you need to import `React` by using this command:
``` javascript
import React from `react`
```

Then, import `ReactDOM` for the `render()` function in which the *HTML* code is specified.

> A style sheet can be used for the specified HTML code as well.


import React from 'react';
require('./style.css');

import ReactDOM from 'react-dom';


ReactDOM.render(
  <p>HelloWorld!</p>,
  document.getElementById('root')
);


import React from 'react';
import { shallow, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

import HelloWorld from './app';

var TestResult = function() {
    this.succeeded = false;
    this.reason = "";
    this.input = "";
    this.expected_output = "";
    this.actual_output = "";
}

export const executeTests = function() {

  var results = [];

  result = new TestResult();
  result.input = 'HelloWorld Component';
  result.expected_output = "span containing text 'Hello World'"

  let wrapper = shallow(<HelloWorld />);

  // Call your Challenge function here.

  let type = wrapper.type();
  let testSuccessful = true;
  let failureReason;

  if (type !== 'span') {
    testSuccessful = false;
    failureReason = "You need to render exactly one span HTML element";
  } else if (wrapper.props().children != "Hello World") {
     testSuccessful = false;
     failureReason = "You have rendered wrong message in your span element";
  }

  result.actual_output = wrapper.html();

  if (testSuccessful) {
    result.succeeded = true;
    result.reason = "Succeeded"
  } else {
    result.succeeded = false;
    result.reason = failureReason;
  }

  results.push(result);

  return results;
}


React

Dart

Typescript React

Hello World in React 

A "Hello World" program in React involves importing React and ReactDOM to render HTML code for user interfaces.