JSX and the Virtual DOM Slides

What is JSX?

Mixes HTML and JavaScript together
Makes building the UI easier
Is transformed into ReactDom code
Is used everyday in React

Starting JSX

This is JSX Code

ReactDOM.render(
  <h1>Hello, React!</h1>,
  document.getElementById('root')
);

Resulting ReactDOM code

This is the ReactDOM code the JSX creates

ReactDOM.render(React.createElement(
  'h1',
  null,
  'Hello, React!'
), document.getElementById('root'));

Resulting HTML in the DOM

<div id="root">
  <h1>Hello, React!</h1>
</div>

What we learned

JSX feels like HTML (inside of JavaScript)
JSX compiles to ReactDOM code
JSX is a 'syntax extension' to JavaScript
ReactDOM builds the HTML from the virtual DOM

JSX can embed JavaScript expressions

Building a greeter

const user = {
  firstName: 'Ada',
  lastName:  'Lovelace',
  nickName:  'The queen of numbers'
};

function formatName(user) {
  return user.firstName + ' ' + user.lastName;
}

const element = (
  <div>
    <h1>Welcome to React, {formatName(user)}!</h1>
    <h2>{user.nickName}</h2>  
  </div>
  );

ReactDOM.render(
  element,
  document.getElementById('root')
);

After compiling JSX -> JS

const user = {
  firstName: 'Ada',
  lastName:  'Lovelace',
  nickName:  'The queen of numbers'
};

function formatName(user) {
  return user.firstName + ' ' + user.lastName;
}

const element = (
  <div>
    <h1>Welcome to React, {formatName(user)}!</h1>
    <h2>{user.nickName}</h2>  
  </div>
  );

ReactDOM.render(
  element,
  document.getElementById('root')
);

JSX results

JSX is transformed into ReactDOM

Tools like Babel convert JSX to ReactDOM
You can use Babel as a script in your project HTML for development

<script src="https://unpkg.com/babel-standalone@6/babel.min.js">
<script type="text/babel">
console.log( <h1>yo</h1> );
</script>

Example

<html lang="en">
  <head>
    <meta charset="UTF-8">
    <script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>
    <script src="https://unpkg.com/react/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom/umd/react-dom.development.js"></script>
  </head>
  <body>
    <div id="output"></div>

    <!-- Load Babel and React -->
    <!-- Your script here -->
    <script type="text/babel">
      ReactDOM.render(
       <h1>Hello, again React!</h1>,
       document.getElementById('output')
      );
    </script>
  </body>
</html>