03-lists

Step 3 - Lists

The goal of this step is to practice transforming lists of data into lists of components which can be included in JSX. As a result, we'll convert the EmailList component from statically rendering the five EmailListItem components to dynamically rendering an arbitrary list of EmailListItem components. We'll also make use of more advanced prop types.

As always, if you run into trouble with the tasks or exercises, you can take a peek at the final source code.

Restart Setup

If you didn't successfully complete the previous step, you can jump right in by copying the step and installing the dependencies.

Ensure you're in the root folder of the repo:

cd react-workshop

Remove the existing workshop directory if you had previously started elsewhere:

rm -rf workshop

Copy the previous step as a starting point:

cp -r 02-components workshop

Change into the workshop directory:

cd workshop

Install all of the dependencies (yarn is preferred):

# Yarn
yarn

# ...or NPM
npm install

Start the app:

# Yarn
yarn start

# ...or NPM
npm start

After the app is initially built, a new browser window should open up at http://localhost:3000/, and you should be able to continue on with the tasks below.

Tasks

The way that you dynamically render multiple elements in React is by putting those elements in an array and rendering the array of components. This differs from traditional template languages where there is some looping construct (such as ng-repeat) and you specify the loop item to display.

In EmailList.js, pull out the raw data that makes up the three EmailListItem components into an EMAILS const array. Use Array.prototype.map to convert the array of data into an array of components:

const EMAILS = [
  {
    id: 1,
    from: 'alittle0@chronoengine.com',
    subject: 'Mauris lacinia sapien quis libero'
  },
  {
    id: 2,
    from: 'amurray1@mit.edu',
    subject: 'Mauris ullamcorper purus sit amet nulla'
  },
  {
    id: 3,
    from: 'dmccoy2@bluehost.com',
    subject: 'Suspendisse potenti'
  },
  {
    id: 4,
    from: 'raustin3@hexun.com',
    subject: 'Maecenas rhoncus aliquam lacus'
  },
  {
    id: 5,
    from: 'rwagner4@instagram.com',
    subject: 'Pellentesque ultrices mattis odi'
  }
];

export default class EmailList extends PureComponent {
  render() {
    let emailComponents = EMAILS.map((email) =>
      <li key={email.id}>
        <EmailListItem from={email.from} subject={email.subject} />
      </li>
    );

    return (
      <ul className="email-list">
        {emailComponents}
      </ul>
    );
  }
}

Be sure to include the key prop on the <li> elements.

Update EmailListItem to take a single email prop instead of individual props for each email property (don't forget the propTypes!):

export default class EmailListItem extends PureComponent {
  static propTypes = {
    email: PropTypes.shape({
      from: PropTypes.string.isRequired,
      subject: PropTypes.string.isRequired
    }).isRequired
  };

  render() {
    let {email: {from, subject}} = this.props;

    return (
      <div className="email-list-item">
        <span>{from}</span>
        <span>{subject}</span>
      </div>
    );
  }
}

The EmailList component will need to be updated to pass the email prop to EmailListItem:

export default class EmailList extends PureComponent {
  render() {
    let emailComponents = EMAILS.map((email) =>
      <li key={email.id}>
        <EmailListItem email={email} />
      </li>
    );

    return (
      <ul className="email-list">
        {emailComponents}
      </ul>
    );
  }
}

We're starting to make something that visually looks like a list of emails, but it currently isn't styled at all. The app already comes with component CSS files so we just need to associate them with their corresponding JS files so that the elements will be styled. Simply import the component CSS files in EmailList.js and EmailListItem.js:

EmailList.js

import React, {PureComponent} from 'react'
import PropTypes from 'prop-types'

import EmailListItem from './EmailListItem'
import {EMAIL_PROP_TYPE} from './constants'

// import component CSS file
import './EmailList.css'

export default class EmailList extends PureComponent {
  ...

EmailListItem

import React, {PureComponent} from 'react';

import {EMAIL_PROP_TYPE} from './constants';

// import component CSS file
import './EmailListItem.css';

export default class EmailListItem extends PureComponent {
  ...

Exercises

• Move the EMAILS out of EmailList into the top-level App
• Pass EMAILS in App as the emails prop to <EmailList>
• Declare a new emails prop type using PropTypes.arrayOf() in EmailList (you can share common prop types with EmailListItem in a components/constants.js file)
• Use this.props.emails (instead of EMAILS) in the map() within render() of EmailList
• Import component CSS for App.js, EmailForm.js and EmailView.js

Next

Go to Step 4 - Email View.

Resources

• Lists and Keys
• Array.prototype.map

Questions

Got questions? Need further clarification? Feel free to post a question in Ben Ilegbodu's AMA!