React Components Lab

Overview

In this lab, you'll write React components and render them into the DOM.

Note: there is already a bit of code in index.js. Don't remove it: you'll need it to complete the exercise!

First Things First

Make sure to import React and ReactDOM into your /src/index.js file. The code is provided in this lesson, all you need to do is uncomment the lines. Using import, we can access the two necessary node modules for React apps.

import React from 'react' // We need to import react so we can make use of its .component class
import ReactDOM from 'react-dom' // ...and we need to import ReactDOM so we can create and test a virtual DOM with react!

For now, we will program all of our React components in this one file.

As mentioned above, there is some starter code in this file to mount the components. In addition, there are three classes in this file that are extending the React.Component class. These will be our components! In this lab, we will be writing all of our components using the ES6 class syntax: class YourComponent extends React.Component {}

The components in this lab are in a particular order. The OlderCoaster, InFrontOfYou, and ButcherShop

The reason we are exporting them here is so that our testing suite will have access to them.

Deliverables

The OlderCoaster

In index.js, implement your OlderCoaster. It should render the following HTML:

<div class="oldercoaster">
  <p>Two grannies having the time of their life!</p>
  <p>Passengers:</p>
  <ul>
    <li>Agnes</li>
    <li>Muriel</li>
  </ul>
</div>

Don't look too far

In index.js, create another React component called InFrontOfYou. It should render the following HTML:

<div>
  <p>You shouldn't look too far.</p>
  <p>Sometimes, the solution is right in front of you.</p>
</div>

Ye Olde Meat Shoppe

In index.js, create one more React component called ButcherShop. It should render the following HTML:

<div class="butcher-shop">
  <p>Hello! We have the following products for sale today:</p>
  <ul>
    <li>Tenderloin</li>
    <li>Short ribs</li>
    <li>Beef shin</li>
    <li>Ribeye</li>
  </ul>
</div>

With this component, we want to render the products from the BUTCHER_PRODUCTS array already at the top of the index.js file. React supports the rendering of arrays filled with valid JSX, i.e.:

const ROTTEN_MEAT_PRODUCTS = ["Old Fish", "Sweeney Todd", "Tomatoes?"]

const products = [<li>{ROTTEN_MEAT_PRODUCTS[0]}</li>, <li>ROTTEN_MEAT_PRODUCTS[1]</li>, etc...]
render() {
  return (
    <div>
      { products }
    </div>
  )
}

Whenever we want to pass a variable into JSX, we need to wrap it in {}. The brackets tell React to resolve everything within the {} with JavaScript and fill in whatever it returns. This is similar to when we have used string interpolation (i.e. #{@doge.name}, ${choux.hobbies}).

What higher order iterator could we use on BUTCHER_PRODUCTS to return that kind of array structure? When a JSX filled array is passed into a render method, React will automatically unpack it to JSX!

Using Components Within Another Component

Finally, now that we have three functioning components, we want to display them together in the browser.

To do this, we need to place our components together inside a 'parent' component. Using JSX, we can include components within other components by wrapping the class name in < />:

class Example extends Component {
  render() {
    return <div> Hello, I am example </div>
  }
}

class Parent extends Component {
  render() {
    return (
      <div>
        <ExampleComponent />
      </div>
    )
  }
}

Note: Sometimes, we may also see the following structure:

class Parent extends React.Component {
}

This is also valid. We are importing in the Component module ({ Component }) at the top of src/index.js , which allows us to just refer to Component directly, and is done for readability.

In src/index.js, include the three components we've created inside the App component to pass the remaining tests.

Near the bottom of the file, we see a unique statement:

ReactDOM.render(<App />, document.getElementById('root'))

The ReactDOM.render() method takes the top level component, <App />. Since all the other components are included within <App />, they will be handled by React's virtual DOM. The second argument in ReactDOM.render() is the location within the real DOM where React steps in on a web page.

Look in the Browser!

Once you've got the four components written, run learn to confirm you've passed the tests. With everything working, we can now take a look and see these components in action.

While its important to get used to reading React code and asserting its functionality directly, (it's just JavaScript, after all!), we should also make sure our React application looks the way we would like in the browser. In order to do this, serve our application by running npm start. Thereafter, we are able to inspect our results in the browser at whatever port it announces it's running on.

Resources

• React Documentation: Components

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