TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It offers classes, modules, and interfaces to help you build robust components.
Next.js is a React framework that makes it easy to create production-ready server-rendered apps. It includes features like Automatic code splitting, Static file serving, Routes handling, and Universal rendering.
In this article, we'll learn how to build progressive web applications (PWAs) using TypeScript and Next.js. We'll start by creating a simple PWA that loads a List component from a JSON file. Then, we'll add TypeScript to our project and use the React typings for type-checking our components. Finally, we'll learn how to use Next.js features like code splitting and route prefetching to improve the performance of our PWA.
We'll start by creating a simple Next.js app that loads a List component from a JSON file. The List component will be server-rendered and will include code splitting and route prefetching.
First, let's create a new Next.js project:
npx create-next-app my-app
Next, we need to install the following dependencies:
npm install --save react react-dom next
Now, we can create our List component. Create a new file named List.js and add the following code:
import React from 'react';
const List = ({ items }) => (
<ul>
{items.map(item => (
<li key={item.id}>{item.text}</li>
))}
</ul>
);
export default List;
This component will take an items prop and render a list of items. Each item will have a key and a text.
Next, we need to create a JSON file that contains our list items. Create a new file named listItems.json and add the following code:
[
{ "id": 1, "text": "Item 1" },
{ "id": 2, "text": "Item 2" },
{ "id": 3, "text": "Item 3" }
]
Now, we can import this JSON file in our List.js component:
import listItems from './listItems.json';
Finally, we need to tell Next.js to render our List component on the server. Open the pages/index.js file and replace the contents with the following code:
import React from 'react';
import List from '../components/List';
const IndexPage = () => <List items={listItems} />;
export default IndexPage;
This will render our List component on the server and pass the listItems JSON data to the component as a prop.
Now, if we run our app, we should see our List component being rendered on the page:
npm run dev
Next, we'll add TypeScript to our project and use the React typings for type-checking our components.
First, we need to install the TypeScript compiler:
npm install --save-dev typescript
Then, we need to create a tsconfig.json file in the root of our project. This file will contain our TypeScript configuration. Add the following code to the tsconfig.json file:
{
"compilerOptions": {
"jsx": "react",
"target": "esnext",
"module": "commonjs",
"strict": true
},
"include": ["src"]
}
This configuration will tell the TypeScript compiler to target the latest JavaScript standard (ESNext) and to treat our code as if it were CommonJS modules.
Next, we need to install the React typings:
npm install --save-dev @types/react @types/react-dom
Now, we can rename our List.js component to List.tsx and start using TypeScript. First, we'll add types to our props:
import React from 'react';
interface ListProps {
items: {
id: number;
text: string;
}[];
}
const List: React.FC<ListProps> = ({ items }) => (
<ul>
{items.map(item => (
<li key={item.id}>{item.text}</li>
))}
</ul>
);
export default List;
We've declared an interface for our props called ListProps. This interface defines the shape of our props. We've also added types to our component using the React.FC generic. This generic allows us to specify the type of our props.
Now, if we try to pass an invalid prop to our component, we'll get a type error:
// TypeError: Type '{ items: number[]; }' is not assignable to type 'IntrinsicAttributes & ListProps'.
// Property 'items' does not exist on type 'IntrinsicAttributes & ListProps'.ts(2322)
<List items={[1, 2, 3]} />
Finally, we'll learn how to use Next.js features like code splitting and route prefetching to improve the performance of our PWA.
Next.js includes a feature called code splitting that allows us to split our code into multiple bundles. This way, the browser can download and execute only the code that is required for the current page.
To use code splitting in our List component, we need to use the React.lazy component. This component allows us to dynamically load components at runtime.
First, let's import the React.lazy component:
import React, { lazy } from 'react';
Then, we can use the lazy component to dynamically load our List component:
const List = lazy(() => import('./List'));
Now, our List component will only be loaded when it is needed.
Next.js also includes a feature called route prefetching. This feature allows Next.js to prefetch the code for other pages in the background. This way, when the user navigates to those pages, the code will already be downloaded and the page will load faster.
To use route prefetching, we need to use the Link component from Next.js. This component will create a link to another page in our app.
First, let's import the Link component:
import Link from 'next/link';
Then, we can use the Link component to create a link to another page:
<Link href="/page2" prefetch>
<a>Navigate to page 2</a>
</Link>
This will create a link to the /page2 route in our app. The prefetch prop will tell Next.js to prefetch the code for this route in the background.
In this article, we've learned how to build progressive web applications (PWAs) using TypeScript and Next.js. We've started by creating a simple PWA that loads a List component from a JSON file. Then, we've added TypeScript to our project and used the React typings for type-checking our components. Finally, we've learned how to use Next.js features like code splitting and route prefetching to improve the performance of our PWA.