Introduction to TypeScript

What is TypeScript

TypeScript is an open-source language maintained and developed by Microsoft.

Basically, TypeScript adds additional syntax to JavaScript to support a tighter integration with your editor. Catch errors early in your editor or in your CI/CD pipeline, and write more maintainable code.

We can talk about other TypeScript benefits later, let's see some examples now!

First TypeScript code

Take a look at this code snippet and then we can unpack it together:

type User = {
  name: string;
  age: number;
};

function isAdult(user: User): boolean {
  return user.age >= 18;
}

const justine = {
  name: 'Justine',
  age: 23,
} satisfies User;

const isJustineAnAdult = isAdult(justine);

The first part (with the type keyword) is responsible for declaring our custom object type representing users. Later we utilize this newly created type to create function isAdult that accepts one argument of type User and returns boolean. After this, we create justine, our example data that can be used for calling the previously defined function. Finally, we create a new variable with information on whether justine is an adult.

There are additional things about this example that you should know. Firstly, if we do not comply with the declared types, TypeScript will inform us that something is wrong and prevent misuse. Secondly, not everything must be typed explicitly—TypeScript infers types for us. For example, the variable isJustineAnAdult is of type boolean even if we didn't type it explicitly, and justine would be a valid argument for our function even though we didn't declare this variable as of User type.

How to run TypeScript code

Okay, so we have some TypeScript code. Now how do we run it? There are few possible ways to run TypeScript code, we will cover all of them in the next articles.