Steps

1. How to install a new react project
2. What is a component?
3. What are props?
4. What is state?
5. What are lifecycle functions?
6. How to style things?
7. Advanced things to keep in mind -> form handling, apollo / redux. etc.

1. Installation:

• Install:

npm install -g create-react-app
create-react-app my-app

• Start the app

yarn start

2. Meddling with the code:

• Editing the src/App.js file works. Try it out.

• Let's try the minimal code though. Remove everything under src/ and then, create one index.js file there with the following content:

  import React from 'react'
  import ReactDOM from 'react-dom'
  
  class Home extends React.Component {
    render() {
      return <div>It is alive!</div>
    }
  }
  
  ReactDOM.render(<Home />, document.getElementById('root'))
  

• Let's keep it separated, shall we. Move the class definition to an App.js file.

  • App.js:

    import React from 'react'
    
    class Home extends React.Component {
      render() {
        return <div>It is alive!</div>
      }
    }
    
    export default Home
    

  • index.js:

    import React from 'react'
    import ReactDOM from 'react-dom'
    
    import Home from './App.js'
    
    ReactDOM.render(<Home />, document.getElementById('root'))
    

TAKEAWAY: We can modularize code and abstract away the logic neatly.

3. Components:

• Let's display a list of someone's friends:

  • App.js

    class Home extends React.Component {
      render() {
        return (
          <div>
            <h1>Someone's friends:</h1>
            <ul>
              <li>1</li>
              <li>2</li>
            </ul>
          </div>
        )
      }
    }
    

• Let's create a Friends Component for this.

  • Friends.js

    class Friends extends React.Component {
      render() {
        return (
          <div>
            <h1>Someone's friends:</h1>
            <ul>
              <li>1</li>
              <li>2</li>
            </ul>
          </div>
        )
      }
    }
    
    export default Friends
    

  • Let's use that in our App.js

    import Friends from './Friends.js'
    
    class Home extends React.Component {
      render() {
        return <Friends />
      }
    }
    

TAKEAWAY: Notice how we "modularized" that bit? This is what we refer to as Components. Apart from looking neat, why is this important though? According to React's own definition, Components let you split the UI into independent, reusable pieces, and think about each piece in isolation.

4. Props

• Let's personalize the Friends Component and see.
• Friends.js

  class Friends extends React.Component {
    render() {
      return (
        <div>
          <h1>Sami's friends:</h1>
          <ul>
            <li>1. Kevin.</li>
            <li>2. Neville.</li>
          </ul>
        </div>
      )
    }
  }
  

• Depending on who opens up the home page, we want to show their name and their two friends. So we want something like this for App.js

  class Home extends React.Component {
    render() {
      return <Friends name="Sami" friend1="Kevin" friend2="Neville" />
    }
  }
  

• How do we access these values that we are passing inside the Friends Component? Enter props. Let's replace the Friends component code with this:

  class Friends extends React.Component {
    render() {
      return (
        <div>
          <h1>{this.props.name}'s friends:</h1>
          <ul>
            <li>1. {this.props.friend1}. </li>
            <li>2. {this.props.friend2}. </li>
          </ul>
        </div>
      )
    }
  }
  

TAKEAWAY: Try changing the parameters and see. So, props allow us to send arbitrary data into our components.

5. State

• Let's try and toggle each friend's "friend/unfriend", shall we? Extend the Friends component and add a few buttons that simply shows an alert on clicking.

  class Friends extends React.Component {
    render() {
      return (
        <div>
          <h1>{this.props.name}s friends:</h1>
          <ul>
            <li>
              1. {this.props.friend1}. Status: Friend
              <button onClick={() => alert(this.props.friend1)}>Go</button>
            </li>
            <li>
              2. {this.props.friend2}. Status: Friend
              <button onClick={() => alert(this.props.friend2)}>Go</button>
            </li>
          </ul>
        </div>
      )
    }
  }
  

• We obviously can't have the status hardcoded there since when we click the button, we want the status to change. How do we store the status? Enter state. Let's start by defining the states of our friends first. We define that in the constructor.

  class Friends extends React.Component {
    constructor(props) {
      super(props)
      this.state = {
        statusFriend1: 'Friend',
        statusFriend2: 'Friend'
      }
    }
    render() {
      return (
        <div>
          <h1>{this.props.name}s friends:</h1>
          <ul>
            <li>
              1. {this.props.friend1}. Status: Friend
              <button onClick={() => alert(this.props.friend1)}>Go</button>
            </li>
            <li>
              2. {this.props.friend2}. Status: Friend
              <button onClick={() => alert(this.props.friend2)}>Go</button>
            </li>
          </ul>
        </div>
      )
    }
  }
  

• Let's display the statuses from the state instead of the hardcoded ones.

  render() {
    return (
      <div>
        <h1>{this.props.name}s friends:</h1>
        <ul>
          <li>
            1. {this.props.friend1}. Status: {this.state.statusFriend1}
            <button onClick={() => alert(this.props.friend1)}>Go</button>
          </li>
          <li>
            2. {this.props.friend2}. Status: {this.state.statusFriend2}
            <button onClick={() => alert(this.props.friend2)}>Go</button>
          </li>
        </ul>
      </div>
    )
  }
  

• Nice. For each friend, we want to toggle the current state. So we'll add a function that checks the current state, and toggles it accordingly. And we'll replace the alert call we had with our function.

  class Friends extends React.Component {
    constructor(props) {
      super(props)
      this.state = {
        statusFriend1: 'Friend',
        statusFriend2: 'Friend'
      }
    }
  
    toggleStatusFriend(friend) {
      if (friend === 'friend1') {
        if (this.state.statusFriend1 === 'Friend') {
          this.setState({ statusFriend1: 'Not Friend' })
        } else {
          this.setState({ statusFriend1: 'Friend' })
        }
      } else {
        if (this.state.statusFriend2 === 'Friend') {
          this.setState({ statusFriend2: 'Not Friend' })
        } else {
          this.setState({ statusFriend2: 'Friend' })
        }
      }
    }
  
    render() {
      return (
        <div>
          <h1>{this.props.name}s friends:</h1>
          <ul>
            <li>
              1. {this.props.friend1}. Status: {this.state.statusFriend1}
              <button
                onClick={() => this.toggleStatusFriend('friend1')}}
              >
                Go
              </button>
            </li>
            <li>
              2. {this.props.friend2}. Status: {this.state.statusFriend2}
              <button
                onClick={() => this.toggleStatusFriend('friend1')}}
              >
                Go
              </button>
            </li>
          </ul>
        </div>
      )
    }
  }
  

• Try clicking the button. It should toggle the status.

• You should ALWAYS use setState while modifying a state. The reason why the status changed on the browser was because React refreshed the Component detecting that a state changed had occurred. React will only detect that if you use setState to set the value of a state and not if you simply assign the value like this.state.statusFriend1 = 'Not Friend'.

• While the example demonstrates the use of states, you should always think of state as something specific to that component. In the real world, the "friend status" would be updated on the server and not just managed in the UI.

TAKEAWAY: In React's own words: props (short for “properties”) and state are both plain JavaScript objects. While both hold information that influences the output of render, they are different in one important way: props get passed to the component (similar to function parameters) whereas state is managed within the component (similar to variables declared within a function).

• PS: Has something already irked you about the above code? If yes, then you have already grasped the idea of components. A component let's you build "resuable" UI elements. Try converting each "Friend" up there into their own components so that we don't do the 1, 2 business.

6. Lifecycle functions

• Think of these as optional pitstops that React takes on the way to rendering the component and as soon as after the component has rendered. (Image courtesy https://hackernoon.com/reactjs-component-lifecycle-methods-a-deep-dive-38275d9d13c0)

  1. Initialization - constructor and defaultProps.
  2. Mounting - componentWillMount, render and then componentDidMount.
  3. Updating - shouldComponentUpdate, componentWillUpdate, render and then componentDidUpdate. If new props are sent to the component, then componentWillReceiveProps deals with that.
  4. Unmounting - componentWillUnmount

7. Styles

• Let's make our page look good (koff koff), shall we? For starters, we are throwing in some inline CSS.

  render() {
    return (
      <div style={{ textAlign: 'center' }}>
        <h1>{this.props.name}s friends:</h1>
        <ul style={{ display: 'inline-block', textAlign: 'left' }}>
          <li>
            1. {this.props.friend1}. Status: {this.state.statusFriend1}
            <button onClick={() => this.toggleStatusFriend('friend1')}>
              Go
            </button>
          </li>
          <li>
            2. {this.props.friend2}. Status: {this.state.statusFriend2}
            <button onClick={() => this.toggleStatusFriend('friend2')}>
              Go
            </button>
          </li>
        </ul>
      </div>
    )
  }
  

• See the style={{}} construct there? While you "can" use it, it SHOULD NOT be your primary choice of styling your website. You should create a separate css file and put your styles there. To demonstrate, create a Friends.css file with the following.
  • Friends.css:

    .Row {
      text-align: center;
    }
    

  • Import and use that in your Friends.js file like so:

    import './Friends.css'
    

    render() {
      return (
        <div className="Row">
          <h1>{this.props.name}s friends:</h1>
          <ul style={{ display: 'inline-block', textAlign: 'left' }}>
            <li>
              1. {this.props.friend1}. Status: {this.state.statusFriend1}
              <button onClick={() => this.toggleStatusFriend('friend1')}>
                Go
              </button>
            </li>
            <li>
              2. {this.props.friend2}. Status: {this.state.statusFriend2}
              <button onClick={() => this.toggleStatusFriend('friend2')}>
                Go
              </button>
            </li>
          </ul>
        </div>
      )
    }