[00:00] One thing you'll notice about our client and server setup here is we have two tsconfig.json files and they're both pretty similar. They actually have pretty much exactly the same config all up here except for the server has an extra attribute called lib.

[00:14] It would be really great if we could make a root tsconfig.json file which they could both inherit from. For this we're going to need the extends property inside the tsconfig.json inside the root ones and we're going to have to create a tsconfig.base.json to inherit from.

[00:33] That is the task. Good luck!


We have been working with separate `client` and `server` `tsconfig.json` files, but they are almost identical. The only difference is that the server configuration has an extra `lib` attribute:

```tsx
// client/tsconfig.json
{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "esModuleInterop": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true,
    "isolatedModules": true
  }
}

// server/tsconfig.json
{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "esModuleInterop": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true,
    "isolatedModules": true,
    "lib": [
      "ES2022"
    ]
  },
}
```

In order to reduce redundancy, it would be better if we could create a root `tsconfig.base.json` file that both client and server could inherit from.

## Challenge

Your task is to create a `tsconfig.base.json` that contains the shared configuration, and modify the existing `tsconfig.json` files in the client and server directories to extend this base configuration.

Hint: Look into the `extends` property for `tsconfig.json` files, and note that the path to the base file is resolved relative to the extending `tsconfig.json`.

Make your TypeScript configuration more maintainable by creating a shared tsconfig.base.json file.

[00:00] In the solution here, we have created a tsconfig.base.json. This could be named anything we want to. I kind of just like calling it .base.json because it indicates, first of all, that it's not a working tsconfig. So TypeScript itself won't look at this and go, ooh, I need to use this to reference

[00:18] all of the other TypeScript files. It will pass over it. But we can use it to basically say, inside the client here, we can say that this tsconfig.json, which is something that TypeScript will check, extends this tsconfig.base.json, which lives above it. So this one will just inherit

[00:36] all of the compiler options inside here. Inside the server, too, we basically do the same thing, but we just add in our extra compiler options that we need here. Beautiful stuff. Now, this works really nicely when you have, let's say, a monorepo, so many, many tsconfigs that you all need

[00:55] to reference basically a single one. And this means that you can change a single value inside here, so restrict or no emit or whatever you like, and you can just basically make that inherit throughout the entire project. You can even have multiple of these. For instance, if you're operating in different environments, that's very, very common, too. So the extends property is really nice.

[01:14] Now, make sure, though, that when you do this, that extends, like, extends will only copy the compiler options over, I'm pretty sure. So anything outside of this, like exclude, or like include, for instance, which lets you specify the files that you want to add into your TypeScript compilation, I'm pretty sure they won't be added. It's mainly just for compiler options.

[01:33] But extends, very, very useful in these situations where you have lots of tsconfigs that you just want to have a base version of and then add extra properties to as you need them.


We'll start by creating a `tsconfig.base.json` file, which serves as our base TypeScript configuration.

It's important to note that this is not a working configuration file for TypeScript, and it will not be used to directly reference other TypeScript files. Instead, it acts as a base configuration that other `tsconfig.json` files can extend.

The `tsconfig.base.json` file contains all the compiler options that are common to both the client and server configurations:

```tsx
{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "esModuleInterop": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true,
    "isolatedModules": true,
  },
}
```

Then inside of the `tsconfig.json` file in the `client` directory, we'll use the `extends` keyword to specify that it extends `tsconfig.base.json`. Remember, the files are resolved relative to the extending `tsconfig.json` file, so we need to use `../../` to go up two directories:

```tsx
// client/tsconfig.json
{
  "extends": "../../tsconfig.base.json"
}
```

We do the same in the `server` directory, but with additional compiler options:

```tsx
// server/tsconfig.json
{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "lib": [
      "ES2022"
    ]
  },
}
```

By extending the base configuration, these `tsconfig.json` files inherit all the compiler options from `tsconfig.base.json`.

This approach is particularly useful when working with monorepos, where many `tsconfig.json` files need to reference a single base configuration.

Another benefit of this setup is that it allows you to change a single value in the base configuration and have that change propagate throughout the entire project.

It's important to note that the `extends` property only copies over `compilerOptions` from a `tsconfig.json` file. Other properties like `exclude` or `include`, which specify the files to include in or exclude from TypeScript compilation, won't be added.

If you're using a monorepo, this approach is highly recommended!

Learn how the extends property in TypeScript configuration files helps reduce redundancy.

Extending a Base TypeScript Configuration

Share Configuration Across Multiple tsconfig Files

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Troubleshoot an unexpected token error in the browser when trying to import a TypeScript file.

Browsers are only able to understand JavaScript syntax, so we need to convert TypeScript syntax to JavaScript syntax for browser execution.

Browsers Can't Understand TypeScript Syntax

Unexpected Token Error in the Browser

Use the TypeScript CLI to convert a TypeScript file into a JavaScript file.

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Compile TypeScript to JavaScript with the TypeScript CLI

Convert a TypeScript File into a JavaScript File

Currently we have to manually run the TypeScript CLI every time we make a change. The tsc CLI features a watch mode to do this automatically.

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Use tsc's Watch Mode to Automatically Compile TypeScript Files

Automating TypeScript Compilation

Currently our TypeScript files are compiled to the same directory as our source files. Let's change that!

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Compiling TypeScript Files to a Directory

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Create a new project with Vite and TypeScript to improve upon our current setup.

Configure Vite for a Vanilla TypeScript Project

Use Vite for a Frontend App with TypeScript

Now that we are using Vite to transpile TypeScript files into JavaScript files, the tsc command doesn't seem to do anything at all.

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TypeScript as a Linter

Comparing Vite with tsc

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The tsx CLI tool allows you to quickly run scripts written in TypeScript.

Quickly Create Scripts with tsx

TypeScript in The Build Process

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TypeScript Basic Types

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Optional Function Parameters in TypeScript

Optional Function Parameters

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Add a Default Parameter with `=`

Default Parameters in JavaScript Functions

Annotate the type of object literals to avoid TypeScript errors and improve inference.

The ({ }) Syntax is used for objects in TypeScript so, this doesn't need to be shown.

Annotating with {}

Typing Object Literals

Object property types can be made optional, allowing for flexibility in the shape of objects.

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Specifying Optional Properties

Making Object Property Types Optional

Having a single source of truth for type definitions in TypeScript functions helps to reduce duplication and make changes in the future easier.

The `type` keyword allows us to reference a type by a different name. This is useful when we want to consolidate multiple types into a single type alias.

Creating `type` Aliases

A Single Source of Truth for Type Definitions

To add an array to an object, we need to define the type of items the array contains.

Learn about the two different syntaxes for defining arrays in TypeScript.

Two Syntaxes for Arrays

Add an Array to an Object

When working with arrays of objects in TypeScript, you need to define the type properly.

There are few different ways in which an array of objects can be expressed

Representing an Array of Objects

Arrays of Objects in TypeScript

Update rest parameters to specify the type of arguments being passed into a function in TypeScript.

Learn how to use rest parameters to pass an indefinite number of arguments of the same type to a function in TypeScript.

Using Rest Parameters in TypeScript

Rest Parameters in TypeScript

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Using Tuple Syntax in TypeScript

Tuples for Precise Array Structures in TypeScript

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The Dangers of Using "any"

The Controversial `any` Type

How to make sure a function and its parameters and return types fit certain criteria, and how to annotate functions passed as arguments

Type aliases can be used to annotate function types for arguments, callbacks, and return values to enforce type safety and enable proper inference.

Function Types for Type Aliases in TypeScript

Function Types

An example of strictly typing a webpage event listener with no return value.

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The `void` Type

Typing an Event Listener

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Hovering Over a Function Call

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TSDoc Comments

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Hitting Control + Space in VS Code will open a list of all sorts of available options such as properties, methods, and DOM events.

The Control + Space Shortcut

Manually Triggering Autocomplete

TypeScript's Approach to Errors

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Quick Renaming in VS Code

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Using Autocomplete and Quick Fix to Import Variables

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VS Code provides a a hotkey for the Organize Imports command, making it quick and easy to clean up your code.

The Organize Imports Hotkey in VS Code

Organizing Imports in Large Files

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Refactoring with Quick Fixes

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Automatic Code Formatting with Prettier

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Restarting the TypeScript Server in VS Code

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Introducing Union Types in TypeScript

Handling Null Values in TypeScript

Understanding union types and assignability is essential to working effectively with TypeScript.

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Combining Literal & Union Types

Restricting Function Parameters

Literal types are assignable based on their literal values.

Literal Type Assignability

Learn how to combine unions in TypeScript to create type aliases with as little duplication as possible.

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Share Configuration Across Multiple tsconfig Files

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