Link to tutorial: https://reactjs.org/tutorial/tutorial.html#overview

• What Is React? React is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small and isolated pieces of code called “components”.

• Passing props is how information flows in React apps, from parents to children.

• Notice how with onClick={() => console.log('click')}, we’re passing a function as the onClick prop. React will only call this function after a click. Forgetting () => and writing onClick={console.log('click')} is a common mistake, and would fire every time the component re-renders.

• In JavaScript classes, you need to always call super when defining the constructor of a subclass. All React component classes that have a constructor should start with a super(props) call.

• After installing React DevTools, you can right-click on any element on the page, click “Inspect” to open the developer tools, and the React tabs (“⚛️ Components” and “⚛️ Profiler”) will appear as the last tabs to the right. Use “⚛️ Components” to inspect the component tree

• To collect data from multiple children, or to have two child components communicate with each other, you need to declare the shared state in their parent component instead. The parent component can pass the state back down to the children by using props; this keeps the child components in sync with each other and with the parent component. Lifting state into a parent component is common when React components are refactored

• The DOM element’s onClick attribute has a special meaning to React because it is a built-in component. For custom components like Square, the naming is up to you. We could give any name to the Square’s onClick prop or Board’s handleClick method, and the code would work the same. In React, it’s conventional to use on[Event] names for props which represent events and handle[Event] for the methods which handle the events.

• There are generally two approaches to changing data. The first approach is to mutate the data by directly changing the data’s values. The second approach is to replace the data with a new copy which has the desired changes

• Immutability makes complex features much easier to implement. Later in this tutorial, we will implement a “time travel” feature that allows us to review the tic-tac-toe game’s history and “jump back” to previous moves. This functionality isn’t specific to games — an ability to undo and redo certain actions is a common requirement in applications. Avoiding direct data mutation lets us keep previous versions of the game’s history intact, and reuse them later.

• Detecting changes in mutable objects is difficult because they are modified directly. This detection requires the mutable object to be compared to previous copies of itself and the entire object tree to be traversed. Detecting changes in immutable objects is considerably easier. If the immutable object that is being referenced is different than the previous one, then the object has changed.

• The main benefit of immutability is that it helps you build pure components in React. Immutable data can easily determine if changes have been made, which helps to determine when a component requires re-rendering. You can learn more about shouldComponentUpdate() and how you can build pure components by reading Optimizing Performance.

• In React, function components are a simpler way to write components that only contain a render method and don’t have their own state. Instead of defining a class which extends React.Component, we can write a function that takes props as input and returns what should be rendered. Function components are less tedious to write than classes, and many components can be expressed this way.

• Unlike the array push() method you might be more familiar with, the concat() method doesn’t mutate the original array, so we prefer it.

Advanced REACT Topics:

• https://reactjs.org/docs/create-a-new-react-app.html#create-react-app
• https://babeljs.io/repl/#?browsers=defaults%2C%20not%20ie%2011%2C%20not%20ie_mob%2011&build=&builtIns=false&corejs=3.21&spec=false&loose=false&code_lz=DwEwlgbgBAxgNgQwM5IHIILYFMC8AiJACwHsAHUsAOwHMBaOMJAFzwD4AoKKYQgRlYDKJclWpQAMoyZQAZsQBOUAN6l5ZJADpKmLAF9gAej4cuwAK5wTXbg1YBJSswTV5mQ7c7XgtgOqEETEgAguTuYFamtgDyMBZmSGFWhhYchuAQrADc7EA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=react&prettier=false&targets=&version=7.20.4&externalPlugins=&assumptions=%7B%7D
• https://github.com/facebook/create-react-app
• https://reactjs.org/docs/optimizing-performance.html#examples
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
• https://learn.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/experimental-features/focus-mode

Tutorial on CodePen:

• https://codepen.io/gaearon/pen/ybbQJX

This project was bootstrapped with Create React App.

In the project directory, you can run:

Runs the app in the development mode.
Open http:https://localhost:3000 to view it in your browser.

The page will reload when you make changes.
You may also see any lint errors in the console.

Launches the test runner in the interactive watch mode.
See the section about running tests for more information.

Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.

The build is minified and the filenames include the hashes.
Your app is ready to be deployed!

See the section about deployment for more information.

Note: this is a one-way operation. Once you eject, you can't go back!

If you aren't satisfied with the build tool and configuration choices, you can eject at any time. This command will remove the single build dependency from your project.

Instead, it will copy all the configuration files and the transitive dependencies (webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point you're on your own.

You don't have to ever use eject. The curated feature set is suitable for small and middle deployments, and you shouldn't feel obligated to use this feature. However we understand that this tool wouldn't be useful if you couldn't customize it when you are ready for it.

You can learn more in the Create React App documentation.

To learn React, check out the React documentation.

This section has moved here: https://facebook.github.io/create-react-app/docs/code-splitting

This section has moved here: https://facebook.github.io/create-react-app/docs/analyzing-the-bundle-size

This section has moved here: https://facebook.github.io/create-react-app/docs/making-a-progressive-web-app

This section has moved here: https://facebook.github.io/create-react-app/docs/advanced-configuration

This section has moved here: https://facebook.github.io/create-react-app/docs/deployment

This section has moved here: https://facebook.github.io/create-react-app/docs/troubleshooting#npm-run-build-fails-to-minify