17 KiB
Next.js
A place for me to learn Next.js
Next.js is developed & maintained by Vercel
Installation (macOS)
Requirements:
- Homebrew already installed
Install nodejs
brew install node@22
Check node version
node -v
Check NPM version
npm -v
If you get some errors:
brew cleanup
Then try again
Create new project
npx create-next-app@latest
Afterwards some questions about the project will be asked. You can leave the settings as default.
Upgrade to newer Next.js version
npx @next/codemod@canary upgrade latest
Run development server
npm run dev
Afterwards the site can be accessed in the browser at http://localhost:3000.
General structure
The whole app is organzied in multiple folders. THe typescript files for the app are stored in src/app.
The code is written in TypeScript.
In package.json are the dependencies saved. The Next.js configuration is saved in next.config.ts.
Each folder in app represents a route of the application, but its only accessable when a page.js or route.js file is contained.
When a folder is named with _ as prefix, it will be ignored by the routing and not accessable from within the application.
Folders in parenthesis (Klammern) while not be show in the route. (https://nextjs.org/docs/app/getting-started/project-structure#organize-routes-without-affecting-the-url-path)
Slugs can be defined by creating a folder in brackets [] like [slug].
Basic tutorial: https://www.youtube.com/watch?v=__mSgDEOyv8
By default the code is executed on the server. When you want to change this behavior the following has to be added to the top of the file:
'use client';
Its possible to render the most parts of an app on the server and some components, like the hover state of the navbar, on the client. Depending on what makes most sense for the application. Thoose components should be move to a separated JS or JSX file.
The main function of the app or just a file is defined by export default.
The layout of the app is defined in layout.js. The content of layout.js is shared between all pages.
Variables in TypeScript can be optional. Optinal variables are declared with a traling question mark (?) after the variables name. Eg. x?: number.
Imports
When importing function and components from other files, there can be named & default imports. Default imports are when you import the default function of a file which was defined by export default function.
Default import
import LatestInvoices from '../ui/dashboard/latest-invoices';
Named import
import { fetchRevenue } from '../lib/data';
Styling
In global.css some global CSS styling rules were defined. Usally this file is imported in the root layout of the app layout.js/layout.jsx/layout.tsx.
Commonly TailwindCSS is used with Next.js for easier stylings. This can be recognized in the beginning of the global.css-File:
@tailwind base;
@tailwind components;
@tailwind utilities;
As an alternative to TailwindCSS also CSS modules can be used for styling. There you would create a own CSS file for every component which needs styling and only import those into the project. More details about that can be found in the Next.js docs.
Additionaly there are other, less popular methods for styling your Next.js app like Sass or CSS-in-JS libraries. And, because in the end just normal CSS is rendered, you can use any styling solution you want/already know too with Next.js.
TailwindCSS
Tailwind is a CSS framework, which enables you to style the whole website without ever leaving the HTML or Next.js code. You never have to touch a CSS file. All styling is done via predefined CSS classes.
When using VScode as Editor the Tailwind CSS IntelliSense should be installed. It enables autofill for Tailwind css classes aund adds preview of the css behind a class when hovering over it. It improves the development process with TailwindCSS a lot.
The styling is applied when adding a css class to an HTML object.
<div className="fixed top-0"></div>
When non existing tailwind class matches the value you need, a custom value can be assigend, which will automatically be generated by tailwind on build.
<div className="top-[-27px]"></div>
Common classes
| class | what it does |
|---|---|
| top-0 | top: 0; |
| left-0 | left: 0; |
| w-0 | width |
| h-0 | height |
| m-0 | margin |
| mx-auto | margin-inline: auto; |
| p-0 | padding |
| flex | display: flex; |
| h-screen | 100vh; -> viewport height |
| bg-gray-900 | background-color |
| text-white | text color |
| shadow-lg | adds a nice shadow (different variantes are available) |
| rounded-3xl | border-radius |
| transition-all | add a transition to every property that changes |
| hover: | Adds class on hover state |
| group | defines a parent element for a group |
| group-hover: | adds a class on hover over the parent of the group |
| dark: | only apply styling in dark mode |
| md: | media query for desktop devices |
| hidden | display: none; |
| block | display: block; |
Tailwind uses a custom spacing scale. The translation table can be found here.
To specify a hover state in tailwind just add a prefix of hover: in front of the styling class.
<div className="hover:bg-green-600 hover:text-white"></div>
When having a lot of styling on a element it can make sense to create a custom css class combining thoose tailwind classes. This can be done by adding the following to globals.css:
@layer components{
.sidebar-icon{
@apply relative flex items-center justify-center
h-12 w-12 mt-2 mb-2 mx-auto shadow-lg
bg-gray-800 text-green-400
hover:bg-green-600 hover:text-white;
}
/* more custom classes... */
}
With @apply other css classes can be applied to an element.
With a group in tailwind its possible to change the state of an child based on the parent like on hover over the parent. But groups don't work when using @apply in css.
The class group has to be added to the parent element. Then a connected hover action can be added to the child via group-hover:<CLASS>.
Example:
<div className="sidebar-icon group">
{icon}
<span className="sidebar-tooltip group-hover:scale-100">
{text}
</span>
</div>
Clsx
clsx is a library which adds the possibility to toggle css classes based on JS conditions. This is useful to change a styling depending on the value of a state.
React Icons
React Icons is a easy way to import the most popular icons into a react project.
It can be installed via npm.
npm install react-icons --save
Now the icons can be used after importing them. Each icon is a custom react component.
import { FaPlay } from "react-icons/fa";
<FaPlay />
Fonts
Fonts are managed in the file /app/ui/fonts.ts. Next.js is be default able to import fonts from Google Fonts. After importing a font the subset has to be defined. In my case its the latin subset.
import { Inter } from 'next/font/google';
export const inter = Inter({subsets: ['latin'], weight: ['400', '700']});
Afterwards the font can be added to the layout.tsx so its visible all over the application.
There also a className has to be added to the body, so that the font will be rendered.
import {inter} from '@/app/ui/fonts';
export default function RootLayout({
children,
}: {
children: React.ReactNode;
}) {
return (
<html lang="en">
<body className={`${inter.className} antialiased`}>{children}</body>
</html>
);
}
The same way other fonts can be imported and also just applied on single objects.
Images
Next.js comes with a built-in image component, which does many image optimizations like serving images as webp or avif where possible, automatically.
The componennt is called <Image>.
Example usage:
import Image from 'next/image';
export default function Page() {
return (
<Image
src="/hero-desktop.png"
width={1000}
height={760}
className="block"
alt="just an example"
/>
);
}
The width and height should be specified to prevent layout shift - the values set are just used for defining the right aspect ratio - Next.js decides by itself which size has to be rendered.
Layouts
In a layout.tsx file the layout of a page with all their subpages is defined. The files has to return a Layout component on the default function. The children should be imported and shown on the layout, else they won't be visible anywhere.
Example layout.tsx
import SideNav from "@/app/ui/dashboard/sidenav";
export default function Layout({children}: {children: React.ReactNode}){
return (
<div className="flex h-screen flex-col md:flex-row md:overflow-hidden">
<div className="w-full flex-none md:w-64">
<SideNav />
</div>
<div className="flex-grow p-6 md:overflow-y-auto md:p-12">
{ children }
</div>
</div>
);
}
Links
By using the <Link /> component instead of the HTML tag <a> you can to client-side-navigation without a full page reload.
import Link from 'next/link';
export default function NavLinks() {
return (
<Link
key={link.name}
href={link.href}
className="flex h-[48px] grow items-center justify-center gap-2 rounded-md bg-gray-50 p-3 text-sm font-medium hover:bg-sky-100 hover:text-blue-600 md:flex-none md:justify-start md:p-2 md:px-3"
>
<LinkIcon className="w-6" />
<p className="hidden md:block">{link.name}</p>
</Link>
);
}
Next.js prefetches the content of the pages linked via <Link /> so that it can a switch between the pages is faster respectly nearly instant.
To show the currently active link the React hook usePathname can be used. To use conditons for changing the css classes you can use clsx.
Example:
import Link from 'next/link';
import {usePathname} from 'next/navigation';
import clsx from 'clsx';
export default function NavLinks() {
const pathname = usePathname();
return (
<>
{links.map((link) => {
const LinkIcon = link.icon;
return (
<Link
key={link.name}
href={link.href}
className={clsx(
"flex h-[48px] grow items-center justify-center gap-2 rounded-md bg-gray-50 p-3 text-sm font-medium hover:bg-sky-100 hover:text-blue-600 md:flex-none md:justify-start md:p-2 md:px-3",
{
'bg-sky-100 text-blue-600': pathname === link.href,
},
)}
>
<LinkIcon className="w-6" />
<p className="hidden md:block">{link.name}</p>
</Link>
);
})}
</>
);
}
Data rendering behaviors
There are two ways of fetching data in Next.js.
- static rendering
- dynamic rendering
Static rendering means that data is fetch while building the app or when the data is revalidating. On each access the cached data will be served. This has the advantage, that the server load can be reduced and the app is faster. Also it has advantages in point of SEO, because there has nothing to be loaded from the server except the page itself.
But this approach isn't useful when personalized data should be shown. There comes dynamic rendering into play. Dynamic rendering enables to render real time data and personalized content for each user. It's also possible to show infos about the request.
Data streaming
Data streaming enables you to transfer data to the client in more smaller chunks instead of one full package. So the users see the content, that is already ready and in the background the rest is loaded. So the app feels faster and the user can begin using it earlier. Also the data can be rendered in parellel, instead of waiting until each request is finished.
By adding a loading.tsx-File with a Loading() component to the app, the streaming can be enabled.
export default function Loading(){
return <div>Loading...</div>;
}
The component Loading() is shown as a fallback while the "real" content is loaded.
Instead of ugly text a skeleton can be implemented. This has the advantage that the user knows where he can expect content and layout shift is minimized.
This loading behaviour is applied to all subpages of the folder its defined in. To prevent this the files, on which it should be appended, can be moved inside a folder in parenthesis. Folders with parenthesis allows to group pages logical, without affecting the URL path.
With Suspense its also possible to just add a skeleton to one component. Then the data fetching process has to be a part of the component. To use Suspense the component has to be wrapped inside it.
import { Suspense } from 'react';
import { RevenueChartSkeleton } from '@/app/ui/skeletons';
export default async function Page(){
return (
<main>
<div className='mt-6 grid grid-cols-1 gap-6 md:grid-cols-4 lg:grid-cols-8'>
<Suspense fallback={<RevenueChartSkeleton />}>
<RevenueChart />
</Suspense>
<LatestInvoices latestInvoices={latestInvoices} />
</div>
</main>
);
}
When multiple components should load at the same time, they should be moved in a own component and then be put into Suspense.
Search function
When you want to implement a search function the following Next.js hooks are benefical. When implementing the search feature the search query should be kept in the URL parameters. This makes it easier to get the search query and also allows users to bookmark or share a URL with a specific search term. The search filed should be implemented on the client side, so that the URL parameters easily can be changed.
Example implementation of a search component (client side)
'use client';
import { MagnifyingGlassIcon } from '@heroicons/react/24/outline';
import { useSearchParams, useRouter, usePathname } from 'next/navigation';
export default function Search({ placeholder }: { placeholder: string }) {
const searchParams = useSearchParams();
const pathname = usePathname();
const { replace } = useRouter();
function handleSearch(term: string){
const params = new URLSearchParams(searchParams);
if (term){
params.set('query', term);
}
else{
params.delete('query');
}
replace(`${pathname}?${params.toString()}`);
}
return (
<div className="relative flex flex-1 flex-shrink-0">
<label htmlFor="search" className="sr-only">
Search
</label>
<input
className="peer block w-full rounded-md border border-gray-200 py-[9px] pl-10 text-sm outline-2 placeholder:text-gray-500"
placeholder={placeholder}
onChange={(e) => {
handleSearch(e.target.value);
}}
defaultValue={searchParams.get('query')?.toString()}
/>
<MagnifyingGlassIcon className="absolute left-3 top-1/2 h-[18px] w-[18px] -translate-y-1/2 text-gray-500 peer-focus:text-gray-900" />
</div>
);
}
When implementing a feature that requires access to the search parameters it depends where the code is excuted. To access the search parameters on the client side useSearchParams() from 'next/navigation' is used. On the server's side you need to pass the prop searchParams to the according function.
Server side example
export default async function Page(props: {
searchParams?: Promise<{
query?: string;
page?: string;
}>;
}){
const searchParams = await props.searchParams;
const query = searchParams?.query || '';
const currentPage = Number(searchParams?.page) || 1;
return (
// return your components
)
}
By implementing a search function this way, every time a user starts typing the search will be queried on each keystroke. This ressolves into a lot requests and unneeded requests. To change this behaviour Debouncing can be implemented. Deboucing implements a limit to the rate how many queries can be fired.
Debouncing can be implemented in a lot of ways. There is a library named use-debounce which does it for you. To use it, the search function has to be wrapped into a debounced callback. Here a simple example:
const handleSearch = useDebouncedCallback((term) => {
console.log(`Searching... ${term}`)
const params = new URLSearchParams(searchParams);
if (term){
params.set('query', term);
}
else{
params.delete('query');
}
replace(`${pathname}?${params.toString()}`);
}, 300);
Then before the partenthisis a time to wait before firing the request can be set. In the example it was 300ms.