React

Quick Reference

Variables

 const myVar = (
   <h1>Love it</h1>
 );

Maps

 // Only do this if items have no stable IDs
 
 const todo = ["fix", "syntax", "highlighting"];
 const todoItems = todos.map((todo, index) =>
 <li key={index}>
   {todo.text}
 </li>
);

Component Example

import React, {Component} from 'react';
import ReactDOM from 'react-dom'; 

class Parent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {name: "Frarthur"};
  }
  render() {
    return <div></div>;
  }  
};

Passing Props to child

Parent.json

import React from 'react';
import ReactDOM from 'react-dom';
import { Child } from './Child';

class Parent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { name: 'Frarthur' };
  }

  render() {
    return <Child name={this.state.name} />;
  }
}

ReactDOM.render(<Parent />, document.getElementById('app'));

Child.json

import React from 'react';

export class Child extends React.Component {
  render() {
    return <h1>Hey, my name is {this.props.name}!</h1>;
  }
}

Forms

You can capture import using the React.createRef() e.g.

class Form extends React.Component
{
   userNameInput = React.createRef();

   handleSubmit = (event) => {
     event.preventDefault()
     console.log(userNameInput.current.value)
   }
   render()
   {
       return (
           <form onSubmit={this.handleSubmit} >
               <input 
                   type="text"
                   placeHolder="background text"
                   ref={this.userNameInput}
                   required
               />
           />
       ) 
    
   }
}

Binding a function

import React from 'react';
import ReactDOM from 'react-dom';
import { Video } from './Video';
import { Menu } from './Menu';

const VIDEOS = {
  fast: 'https://s3.amazonaws.com/codecademy-content/courses/React/react_video-fast.mp4',
  slow: 'https://s3.amazonaws.com/codecademy-content/courses/React/react_video-slow.mp4',
  cute: 'https://s3.amazonaws.com/codecademy-content/courses/React/react_video-cute.mp4',
  eek: 'https://s3.amazonaws.com/codecademy-content/courses/React/react_video-eek.mp4'
};

class App extends React.Component {
  constructor(props) {
    this.chooseVideo = this.chooseVideo.bind(this);
    super(props);
    this.state = { 
      src: VIDEOS.fast 
    };
  }
  
  chooseView(newView)   {
    this.setState({
      src: VIDEOS[newVideo]
    });
  }
  render() {
    
    return (
      <div>
        <h1>Video Player</h1>
        <Menu chooseVideo={this.chooseView()} />
        <Video src={this.state.src} />
      </div>
    );
  }
}

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

import React from 'react';

export class Menu extends React.Component {
  
  constructor() {
    super(props)
    this.handleClick = this.handleClick.bind(this);
  }
  
  handleClick(e) {
    var text = e.target.value;
    this.props.chooseView(text);
  }
  
  render() {
    return (
      <form OnClick={this.handleClick}>
        <input type="radio" name="src" value="fast" /> fast
        <input type="radio" name="src" value="slow" /> slow
        <input type="radio" name="src" value="cute" /> cute
        <input type="radio" name="src" value="eek" /> eek
      </form>
    );
  }
}

import React from 'react';

export class Video extends React.Component {
  render() {
    return (
      <div>
        <video controls autostart autoPlay muted src={this.props.src} />
      </div>
    );
  }
}

Inline Styling

React needs double quotes to inject style in JSX e.g.

import React from 'react';
import ReactDOM from 'react-dom';

const styleMe = <h1 style={{ background: 'lightblue', color: 'darkred' }}>Please style me! I am so bland!</h1>;

ReactDOM.render(
	styleMe, 
	document.getElementById('app')
);

Another example

mport React from 'react';
import ReactDOM from 'react-dom';
const styles = {
  background: 'lightblue',
  color:      'darkred',
  marginTop: '100px',
  fontSize: '50px'
}

const styleMe = <h1 style={styles}>Please style me! I am so bland!</h1>;

ReactDOM.render(
	styleMe, 
	document.getElementById('app')
);

You can write px styles without quotes e.g.

const styles = {
  background: 'lightblue',
  color:      'darkred',
  marginTop: 100,
  fontSize: 50
}

Stateless Classes

A component class written in the usual way:

export class MyComponentClass extends React.Component {
  render() {
    return <h1>Hello world</h1>;
  }
}

// The same component class, written as a stateless functional component:
export const MyComponentClass = () => {
  return <h1>Hello world</h1>;
}

You can pass the properties from the container class like this

import React from 'react';

export const GuineaPigs = (props) => {
  let src = props.src;
  return (
    <div>
      <h1>Cute Guinea Pigs</h1>
      <img src={src} />
    </div>
  );
}

Prototypes

Add them at the bottom so people can see how to use the code

import React from 'react';

export class BestSeller extends React.Component {
  render() {
    return (
      <li>
        Title: <span>
          {this.props.title}
        </span><br />
        
        Author: <span>
          {this.props.author}
        </span><br />
        
        Weeks: <span>
          {this.props.weeksOnList}
        </span>
      </li>
    );
  }
}

// This propTypes object should have
// one property for each expected prop:
BestSeller.propTypes = {
  title: React.PropTypes.string.isRequired,
  author: React.PropTypes.string.isRequired,
  weeksOnList: React.PropTypes.number.isRequired,
};

And a render example

import React from 'react';
import ReactDOM from 'react-dom';
import { BestSeller } from './BestSeller';

export class BookList extends React.Component {
  render() {
    return (
      <div>
        <h1>Best Sellers</h1>
        <div>
          <ol>
            <BestSeller 
              title="Glory and War Stuff for Dads" 
              author="Sir Eldrich Van Hoorsgaard" 
              weeksOnList={10} />
            <BestSeller 
              title="The Crime Criminals!" 
              author="Brenda Sqrentun" 
              weeksOnList={2} />
            <BestSeller
              title="Subprime Lending For Punk Rockers" 
              author="Malcolm McLaren" 
              weeksOnList={600} />
          </ol>
        </div>
      </div>
    );
  }
}

ReactDOM.render(<BookList />, document.getElementById('app'));

And for stateless functions

import React from 'react';

export class GuineaPigs extends React.Component {
  render() {
    let src = this.props.src;
    return (
      <div>
        <h1>Cute Guinea Pigs</h1>
        <img src={src} />
      </div>
    );
  }
}

GuineaPigs.propTypes = {
  src: React.PropTypes.string.isRequired
};

Form Example where we track the input value

import React from 'react';
import ReactDOM from 'react-dom';

export class Input extends React.Component {
  constructor(props) {
    super(props);
    
    this.state = { userInput: '' };
    
    this.handleUserInput = this.handleUserInput.bind(this);
  }
  
  handleUserInput(e) {
    this.setState({userInput: e.target.value});
  }

  render() {
    return (
      <div>
        <input type="text" onChange={this.handleUserInput} value={this.state.userInput} />
        <h1>{this.state.userInput}</h1>
      </div>
    );
  }
}

ReactDOM.render(
	<Input />,
	document.getElementById('app')
);

Type Script

This is another way to valid props

 import * as React from "react";

 interface Props {
   name: string
 }

 function Greeting(props : Props) {
    return (
        <h1>Hello {props.name}</h1>
    )
 }

Lifecycle

A component “mounts” when it renders for the first time. This is when mounting lifecycle methods get called.

There are three mounting lifecycle methods:

• componentWillMount
• render
• componentDidMount

There are five updating lifecycle methods:

• componentWillReceiveProps
• shouldComponentUpdate
• componentWillUpdate
• render
• componentDidUpdate

Some words of wisdom

A React component should use props to store information that can be changed, but can only be changed by a different component.

A React component should use state to store information that the component itself can change.