Setting Up TypeScript

To begin using TypeScript, you first need to install Node.js. You can opt for either the Long Term Support (LTS) version or the latest feature release. After installation, verify your Node.js version by typing node -v and check your npm version with npm -v in your terminal.

Next, install TypeScript globally using npm with the command:

npm install -g typescript

After the installation, you will have access to the TypeScript Compiler via the tsc command. It's a good practice to check your installed TypeScript version as well.

With your setup complete, let's delve into the workings of TypeScript.

TypeScript Compiler

Start by creating an index.ts file in your project directory. Insert a simple console.log statement and compile the TypeScript file using tsc index.ts. You will notice that a corresponding .js file is generated, as the console.log syntax is standard JavaScript, requiring no modifications during the compilation.

By default, TypeScript compiles to ES3, which lacks support for async/await syntax. If you try to write an async function and compile it, the output JavaScript will be significantly larger to accommodate the async/await functionality.

To customize the version used for compilation, create a tsconfig.json file. Upon saving this file and running the tsc command again, you may find that the generated JavaScript closely mirrors the TypeScript file, provided you set the compiler option to esnext, which includes async/await support.

You can also enable the watch option, allowing the compiler to monitor file changes and compile in real-time, and specify libraries to include automatic typings for certain DOM methods, reducing compilation errors.

{

"compilerOptions": {

"watch": true,

"lib": ["esnext"]

}

}

Integrating Third-Party Libraries

As you advance in TypeScript development, you may want to incorporate third-party libraries, such as lodash. Install it using:

npm install lodash

When you try to import lodash into your TypeScript file, you might encounter errors indicating that the module declaration is unrecognized, resulting in a lack of intellisense and typing support.

Fortunately, the TypeScript community maintains type definitions for many popular libraries. To resolve the issue, run the following command:

npm install -D @types/lodash

Once this is done, the errors will disappear, restoring intellisense and autocomplete for lodash.

TypeScript Basics

Understanding how to properly type your code is essential in TypeScript. There are two primary methods: implicit and explicit typing. While using any type offers flexibility, it undermines the benefits of TypeScript, as the editor won't catch type errors for such variables.

You can also define custom types, limiting the parameters accepted by a field. For example, you can restrict the myColor variable to only accept predefined options.

Creating an interface allows you to enforce strict typing on objects, helping identify any incorrect fields. If necessary, you can also add optional fields for flexibility, but overusing this feature can lead to redundancy and increased error risks.

Strongly Typed Functions

In addition to variable typing, you can enforce strong typing in functions. Without declared types, the IDE cannot catch errors when an unexpected argument is passed. However, by specifying argument and return types, type mismatches will be flagged immediately by the IDE, enabling swift corrections.

function add(a: number, b: number): number {

return a + b;

}

For functions that do not return a value, you can indicate the return type as void.

Strongly Typed Arrays

When declaring arrays, using a general type allows any data type to be pushed into them. However, by strongly typing the array, the IDE will flag any attempts to add incorrect types, enhancing type safety.

TypeScript Generics

Generics in TypeScript enable you to define a class with a generic type, ensuring compatibility when extending or using that class in other contexts.

class Box<T> {

contents: T;

constructor(value: T) {

this.contents = value;

}

}

This allows classes or variables that utilize this generic class to specify their own types, maintaining flexibility without compromising type safety.