Narrow Types

[00:00] All right, we're going to try the exponentiation operator here and we should get an error, but we're not. If I save this, the application blows up. So let's come up here and let's limit the operator to only these specific strings. So we're going to use union. It can be plus or minus

[00:19] or multiply or divide. And with that now, we no longer have an error here because TypeScript knows, so I know what the operations is. It's these things. I know what the operator could possibly be. It's only those things and that matches up. So we don't have an error here anymore. And down here, we do get an error for that, which is nice. So if I get rid of that

[00:39] and change that back to plus, then we get our application working exactly as we want. So we are doing swimmingly. So this is maybe not the most efficient way to do this. We're going to talk about that here in a second, but it does solve our immediate problem.

[00:55] And if we were to take this a little bit further, which we will, then we can make the experience even better for us. But as far as the users of our components are concerned, this is a really nice experience. In fact, we even get some autocomplete now. Look at that. Oh, snap,

[01:13] because we have a limited subset. We've narrowed the possible values. And so our editor can say, hey, here are the possible values you can enter, which I think is pretty stellar. So good job.

[00:00] So we've made things much better, so we don't accidentally pass a string or whatever to these different things. But we only have some very specific operators here. You can only do plus, minus, multiply, divide based on our operations that we can do up here.

[00:14] And it would be nice if we only allow those, so we would get an error if we tried to do something like this, rather than having to run the application to see that that is not going to work. So, your job is to make the operator more narrowly typed. So right now, it's a broad type.

[00:32] It means we can accept all sorts of different kinds of inputs. You could do, like, any sort of string here. But we want to narrow down the type to just some specific string. So it can be plus, minus, multiply, or divide, and it can't be anything else. So your job is to do that in the most efficient way possible. Have a good time.

Learn everything you need to be effective with the fundamental building blocks of React applications. 

The path of this workshop takes you from the fundamental API of appending DOM nodes, through React's raw APIs, to how JSX compiles into React's methods.

Once you have a firm grasp of what React is doing with creating elements, you'll learn the other tools you need to build webpages like: styling, forms, and inputs. 

But, this isn't just a native web course. 

**You'll be building a strong foundation in React.** 

Learn how to: 

- build reusable components
- leverage TypeScript with React
- catch errors with Error Boundaries
- render arrays properly with the `key` prop. 

When you’re finished, you’ll be prepared to create and use React components to build excellent experiences for your app's users.

## Hello World in JS

You'll start your journey by learning some of the history of how we went from generating HTML on the server and adding JS on top to full-fledged frameworks. 

To learn React you'll be following a similar path and begin by learning how to manually append your own DOM nodes.

I call this "going down to level up." You'll find yourself much more efficient with React if you understand the fundamentals of the DOM and JavaScript!

## Raw React APIs

Before getting into JSX, you'll learn how to work with React and ReactDOM's raw APIs. 

You'll create React elements with `React.createElement` and learn how compose your elements with calls to this function. Then, you'll render the React elements you create using ReactDOM.

## Using JSX

Once you know what React is doing under the hood, you'll be prepared to learn JSX.

This section covers more than just how to write it, you'll also use babel to experiement with how JSX gets compiled to the raw React APIs!

## Custom Components

Just like in regular JavaScript, when you want to reuse code, you write functions. If you want to share JSX, you can do that as well. 

In this section you'll learn about how in React, we call these functions "components", the special properties of these functions, and how to 

## TypeScript

> TypeScript is not making your life terrible. It's just showing you how terrible your life already is. 
 
*- Kent C. Dodds*

Getting a solid hold of TypeScript from the get-go will set you up for success. Since React components are just functions, there aren't any special considerations when applying type annotations. 

So, you'll be working on two things:

1. Improving your TypeScript skills
2. Learning the React-specific types available

## Styling

In this section you'll learn about the two primary ways to style React components:

1. Inline styles with the `style` prop
2. Regular CSS with the `className` prop

You'll also learn why React uses a `className` prop instead of `class`. 👀

## Forms

In React, there actually aren't a ton of things you have to learn to interact with forms beyond what you can do with regular DOM APIs and JavaScript.

Here, you'll learn the form markup, build an onSubmit handler, and then create a form action. 

## Inputs

There's a ton of different input types and you're going to learn a lot about them here!

You'll learn about the different text inputs, check boxes, radios, hidden inputs, how to make sure everything is properly labeled and accessible, and setting default values and default checked boxes. 

## Error Boundaries

This is something you want to learn early on. Sometimes things go wrong and we need to handle errors and display useful information to the user. 

An ErrorBoundary component doesn't ship with React by default. So, you'll be importing one from react-error-boundry and then learning how to compose it, and then give the option to the user to reset. 

## Rendering Arrays

In React you can render arrays of elements. One of the tricky parts about it is the `key` prop. 

In this section, you'll learn in detail why React needs the `key` prop to keep track of elements and the nuances of the value that is used. 

Finally, you'll learn a cool trick where the `key` prop is used as a mechanism for resetting elements in the DOM!


Starting with an HTML file and a script, you'll learn React API to build components and manage forms. Learn the fundamentals of building on the web with React.

React Fundamentals

React Fundamentals

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Narrow Types

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