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React makes it painless to create interactive UIs.

Component based.

// book.js
import React from "react";

class Book extends React.Component {
  render() {
    return (
      <h1>{ this.props.title }</h1>
    );
  }
}

export default Book;

// book_list.js
import React from "react";

class BookList extends React.Component {
  render() {
    return (
      { this.props.books.map((book) => {
          <Book title={ book.title } />
        })
      }
    );
  }
}

export default BookList;

// book_list.js
import React from "react";

class BookList extends React.Component {
  constructor() {
    super();

    this.state = {
      books: [{ id: 1, title: "Awesome book" },
              { id: 2, title: "Programming JS" }]
    };
  }

  render() {
    return (
      { this.state.books.map((book) => {
          <Book
            id={ book.id }
            title={ book.title }
          />
        })
      }
    );
  }
}

export default BookList;

• Store - single application state
• Actions - describe what happened in your application
• Reducers - describe how to change the state of your application

1. Single Source of Truth
   • State of the whole application is stored in a single object
2. State Is Read-Only
   • The only way to change the state is to dispatch actions
   • No manual mutations of state
   • All changes are centralised
   • Changes happen one-by-one (no race conditions)
3. Changes are made with pure functions
   • Reducers must be pure functions
   • Splitting reducers (each reducer handles one part of the state)

Actions are plain JS objects. Each action must have a type property.

{
  type: 'HOLD_WORKSHOP',
  subject: 'Redux'
}

Action creators are functions that return actions.

const holdWorkshop = subject => {
  return {
    type: 'HOLD_WORKSHOP',
    subject
  };
};

Actions are dispatched using the store.

store.dispatch(action);
store.dispatch(holdWorkshop);

Reducers are pure functions that return new application state based on dispatched action.

(prevState, action) => newState

const reducer = (state, action) => {
  switch(action.type) {
    case TYPE1: return newState1;
    case TYPE2: return newState2;
    default: return state
  };
};

• Holds whole application state
• Allows access to state via getState
• Allows changing state via dispatch(action)

UNIDIRECTIONAL DATA FLOW

1. Dispatch action
2. Store calls reducers to calculate new state
3. Store saves calculated state
4. Listeners get notified to update their data via getState

1. Making API requests in components and dispatching actions when response is returned (bad)
2. Using middlewares (good)

Using Thunk middlewares:

• put all asynchronous code in action
• action creator returns a function
• middlewares executes code of that function when action is dispatched
• dispatch normal actions based on response of asynchronous action