StevenJL

class CompleteOrder
  def perform
    notify_recipient(order.recipient)
    update_inventory(order.item_number)
    prepare_shippping(order.shipping_address)
  end
  
  private
  
  def order

StevenJL

class User extends React.PureComponent {
  
  // ...
  
  updateUserStatus(status) {
    const { user } = this.state
    
    this.state.user.status = status
  }
  

StevenJL

class User extends React.Component {
  
  // ...
  
  updateUserStatus(status) {
    const { user } = this.state;
    setState({ user: {...user, status: status }})
  }
  
  appendItem(newItem) {

StevenJL

import shallowEqual from 'shared/shallowEqual';
/* 
  shallowEqual is a helper function from the React source code:
  https://github.com/facebook/react/blob/72434a7686035b4af766ee7d06c070d7f5d6a5f2/packages/shared/shallowEqual.js
*/

shouldComponentUpdate(nextProps, nextState) {
  return !shallowEqual(this.props, nextProps) || !shallowEqual(this.State, nextState);
}

StevenJL

import PropTypes from 'prop-types';

Widget.propTypes = {
  extraArray: PropTypes.array.isRequired,
  userNames: PropTyes.arrayOf(PropTypes.string).isRequired,
  userPosts: PropTypes.arrayOf(PropTypes.shape({
    id: PropTypes.number.isRequired,
    title: PropTypes.string.isRequired,
    body: PropTypes.string.isRequired,
    postDate: PropTypes.instanceOf(Date).isRequired

StevenJL

import PropTypes from 'prop-types';

Widget.propTypes = {
  // Specify that prop is an object
  extraData: PropTypes.object.isRequired,
  
  // Specify that prop is an object with certain keys
  userData: PropTypes.shape({
    name: PropTypes.string, 
    age: PropTypes.number

StevenJL

import PropTypes from 'prop-types'

Widget.propTypes = { 
  headerText: PropTypes.string.isRequired,
  widgetCount: PropTypes.number.isRequired,
  isFetchingData: PropTypes.bool.isRequired,
  handlerFunction: PropTypes.func.isRequired,
  createdAt: PropTypes.instanceOf(Date).isRequired,
  optionalText: PropTypes.string
}

StevenJL

import PropTypes from 'prop-types';

class ItemComponent extends React.Component {
  
  // propTypes can be defined inside the Component definition
  static propTypes = {
    name: PropTypes.string.isRequired,
    price: PropTypes.number.isRequired,
    purchaseHandler: PropTypes.func.isRequired
  };

StevenJL

import PropTypes from 'prop-types';

const ItemDiv = ({ name, price, purchaseHandler }) => {
  return(
    <div>
      div> Item:{name} </div>
      div> Price:${price} </div>
      <button onClick={purchaseHandler}> Purchase </button>
    </div>
  )

StevenJL

class ControlledComponent extends React.Component {
  constructor( props) { 
    super(props)
    this.handleSubmit = this.handleSubmit.bind(this) 
  }
  
  handleSubmit(event) { 
    event.preventDefault()
    
    this.props.createAccount(