Porting a Next.js Site to Astro Step-by-Step

June 29, 2023

1,739 words

Astro is a WebDev meta-framework that allows you to build highly performant websites, that, out-of-the-box compile down to 0kb of JavaScript in your bundle.

If your site is a marketing site, or if performance is a substantial concern for your app, it may make sense to migrate from Next.js to Astro - as we at Unicorn Utterances once did.

While Astro provides a good guide of how to migrate from Next.js to Astro (written by yours truly!), I felt it would be helpful to see an expanded step-by-step guide on how to migrate a Pokédex application from Next.js to Astro.

A list of the original 150 pokemon with a picture of each

For the full codebase of the Pokédex application, check the original repo here.

Let's start the migration by changing our layout file to an Astro layout file.

Next base layout to Astro

To start migrating a Next.js layout file from Next.js to Astro, you'll:

  1. Identify the return().

    // _document.jsimport { Html, Head, Main, NextScript } from 'next/document'export default function Document() {    return (        <Html>            <Head lang="en">                <link rel="icon" type="image/svg+xml" href="/favicon.svg" />            </Head>            <body>                <div className="screen">                    <div className='screen-contents'>                        <Main />                    </div>                </div>                <NextScript />            </body>        </Html>    )}

  2. Create Layout.astro and add this return value, converted to Astro syntax.

    Note that:

    • <Html> becomes <html>
    • <Head> becomes <head>
    • <Main /> becomes <slot />
    • className becomes class
    • We do not need <NextScript>
    ---// src/layouts/Layout.astro---<html>    <head lang="en">        <link rel="icon" type="image/svg+xml" href="/favicon.svg" />    </head>    <body>        <div class="screen">            <div class='screen-contents'>                <slot />            </div>        </div>    </body></html>

  3. Import the CSS (found in _app.js)

    In addition to the _document file, the Next.js application has a _app.js file that imports global styling via a CSS import:

    // pages/_app.jsimport '../styles/index.css'export default function MyApp({ Component, pageProps }) {  return <Component {...pageProps} />}

    This CSS import can be moved to the Astro Layout component:

    ---// src/layouts/Layout.astroimport '../styles/index.css'---<html>    <head lang="en">        <link rel="icon" type="image/svg+xml" href="/favicon.svg" />    </head>    <body>        <div class="screen">            <div class='screen-contents'>                <slot />            </div>        </div>    </body></html>

Convert a Next.js getStaticProps Page to Astro

Next up, let's migrate Next.js' getStaticProps method to use Astro's data fetching.

We'll start with a Next.js page that lists the first 151 Pokémon using the REST PokéAPI:

// pages/index.jsimport Link from 'next/link'import Head from 'next/head'import styles from '../styles/poke-list.module.css';export default function Home({ pokemons }) {    return (        <>            <Head>                <title>Pokedex: Generation 1</title>            </Head>            <ul className={`plain-list ${styles.pokeList}`}>                {pokemons.map((pokemon) => (                    <li className={styles.pokemonListItem} key={pokemon.name}>                        <Link className={styles.pokemonContainer} as={`/pokemon/${pokemon.name}`} href="/pokemon/[name]">                            <p className={styles.pokemonId}>No. {pokemon.id}</p>                            <img className={styles.pokemonImage} src={`https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/${pokemon.id}.png`} alt={`${pokemon.name} picture`}></img>                            <h2 className={styles.pokemonName}>{pokemon.name}</h2>                        </Link>                    </li>                ))}            </ul>        </>    )}export const getStaticProps = async () => {    const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")    const resJson = await res.json();    const pokemons = resJson.results.map(pokemon => {        const name = pokemon.name;        // https://pokeapi.co/api/v2/pokemon/1/        const url = pokemon.url;        const id = url.split("/")[url.split("/").length - 2];        return {            name,            url,            id        }    });    return {        props: {            pokemons,        },    }}

Move Next Page Templating to Astro

To start migrating this page to Astro, start with the returned JSX and place it within an .astro file:

---// src/pages/index.astroimport styles from '../styles/poke-list.module.css';---<head>    <title>Pokedex: Generation 1</title></head><ul class={`plain-list ${styles.pokeList}`}>    {pokemons.map((pokemon) => (        <li class={styles.pokemonListItem} key={pokemon.name}>            <a class={styles.pokemonContainer} href={`/pokemon/${pokemon.name}`}>                <p class={styles.pokemonId}>No. {pokemon.id}</p>                <img class={styles.pokemonImage} src={`https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/${pokemon.id}.png`} alt={`${pokemon.name} picture`}></img>                <h2 class={styles.pokemonName}>{pokemon.name}</h2>            </Link>        </li>    ))}</ul>

During the migration to Astro templating, this example also:

  • Imported styles move to the code fence
  • Removed the <> container fragment, as it is not needed in Astro's template.
  • Changed className to a more standard class attribute.
  • Migrated the Next <Link> component to an <a> HTML element.

Now move the <head> into your existing layout.astro file. To do this, we can:

  1. Pass the title property to the layout.astro file via Astro.props
  2. Import the layout file in /src/pages/index.astro
  3. Wrap the Astro page's template in the Layout component
---// src/layouts/Layout.astroimport '../styles/index.css'const {title} = Astro.props;---<html>    <head lang="en">        <link rel="icon" type="image/svg+xml" href="/favicon.svg" />        <title>{title}</title>    </head>    <body>        <div class="screen">            <div class='screen-contents'>                <slot />            </div>        </div>    </body></html>
---// src/pages/index.astroimport styles from '../styles/poke-list.module.css';import Layout from '../layouts/layout.astro';---<Layout title="Pokedex: Generation 1">    <ul class={`plain-list ${styles.pokeList}`}>        {pokemons.map((pokemon) => (            <li class={styles.pokemonListItem} key={pokemon.name}>                <a class={styles.pokemonContainer} href={`/pokemon/${pokemon.name}`}>                    <p class={styles.pokemonId}>No. {pokemon.id}</p>                    <img class={styles.pokemonImage} src={`https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/${pokemon.id}.png`} alt={`${pokemon.name} picture`}></img>                    <h2 class={styles.pokemonName}>{pokemon.name}</h2>                </Link>            </li>        ))}    </ul></Layout>

Move Next Page Logic Requests to Astro

This is the getStaticProps method from the Next.js page:

export const getStaticProps = async () => {    const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")    const resJson = await res.json();    const pokemons = resJson.results.map(pokemon => {        const name = pokemon.name;        // https://pokeapi.co/api/v2/pokemon/1/        const url = pokemon.url;        const id = url.split("/")[url.split("/").length - 2];        return {            name,            url,            id        }    });    return {        props: {            pokemons,        },    }}

This then passes the props into the Home component that's been defined:

export default function Home({ pokemons }) {	// ...}

In Astro, this process is different. Instead of using a dedicated getStaticProps function, move the props logic into the code fence of our Astro page:

---// src/pages/index.astroimport styles from '../styles/poke-list.module.css';import Layout from '../layouts/layout.astro';const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151");const resJson = await res.json();const pokemons = resJson.results.map(pokemon => {    const name = pokemon.name;    // https://pokeapi.co/api/v2/pokemon/1/    const url = pokemon.url;    const id = url.split("/")[url.split("/").length - 2];    return {        name,        url,        id    }});---<Layout title="Pokedex: Generation 1">    <ul class={`plain-list ${styles.pokeList}`}>        {pokemons.map((pokemon) => (            <li class={styles.pokemonListItem} key={pokemon.name}>                <a class={styles.pokemonContainer} href={`/pokemon/${pokemon.name}`}>                    <p class={styles.pokemonId}>No. {pokemon.id}</p>                    <img class={styles.pokemonImage} src={`https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/${pokemon.id}.png`} alt={`${pokemon.name} picture`}></img>                    <h2 class={styles.pokemonName}>{pokemon.name}</h2>                </Link>            </li>        ))}    </ul></Layout>

You should now have a fully working Pokédex entries screen.

Convert a Next.js getStaticPaths Page to Astro

This is a Next.js dynamic page that generates a detail screen for each of the first 151 Pokémon using the REST PokéAPI.

// pages/pokemon/[name].jsimport { useRouter } from 'next/router';import Head from 'next/head'import styles from '../../styles/pokemon-entry.module.css';function capitalize(str) {  return str.charAt(0).toUpperCase() + str.slice(1);}export default function Pokemon({ pokemon }) {  const router = useRouter();  const title = `Pokedex: ${pokemon.name}`;  return (    <>      <Head>        <title>{title}</title>      </Head>      <button onClick={() => router.back()} className={styles.backBtn} aria-label="Go back"></button>      <img className={styles.pokeImage} src={pokemon.image} alt={`${pokemon.name} picture`} />      <div className={styles.infoContainer}>        <h1 className={styles.header}>No. {pokemon.id}: {pokemon.name}</h1>        <table className={styles.pokeInfo}>          <tbody>            <tr>              <th>Types</th>              <td>{pokemon.types}</td>            </tr>            <tr>              <th>Height</th>              <td>{pokemon.height}</td>            </tr>            <tr>              <th>Weight</th>              <td>{pokemon.weight}</td>            </tr>          </tbody>        </table>        <p className={styles.flavor}>{pokemon.flavorText}</p>      </div>    </>  )}export const getStaticPaths = async () => {  const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")  const resJson = await res.json();  const pokemons = resJson.results;  return {    paths: pokemons.map(({ name }) => ({      params: { name },    }))  }}export const getStaticProps = async (context) => {  const { name } = context.params  const [pokemon, species] = await Promise.all([    fetch(`https://pokeapi.co/api/v2/pokemon/${name}`).then(res => res.json()),    fetch(`https://pokeapi.co/api/v2/pokemon-species/${name}`).then(res => res.json())  ])  return {    props: {      pokemon: {        id: pokemon.id,        image: pokemon.sprites.front_default,        name: capitalize(pokemon.name),        height: pokemon.height,        weight: pokemon.weight,        flavorText: species.flavor_text_entries[0].flavor_text,        types: pokemon.types.map(({ type }) => type.name).join(', ')      },    },  }}

Move Next Page Templating to Astro

To start migrating this page to Astro, start with the returned JSX and place it within an .astro file:

---// src/pages/pokemon/[name].astroimport styles from '../../styles/pokemon-entry.module.css';---<Layout title={`Pokedex: ${pokemon.name}`}>  <button onclick="history.go(-1)" class={styles.backBtn} aria-label="Go back"></button>  <img class={styles.pokeImage} src={pokemon.image} alt={`${pokemon.name} picture`} />  <div class={styles.infoContainer}>    <h1 class={styles.header}>No. {pokemon.id}: {pokemon.name}</h1>    <table class={styles.pokeInfo}>      <tbody>        <tr>          <th>Types</th>          <td>{pokemon.types}</td>        </tr>        <tr>          <th>Height</th>          <td>{pokemon.height}</td>        </tr>        <tr>          <th>Weight</th>          <td>{pokemon.weight}</td>        </tr>      </tbody>    </table>    <p class={styles.flavor}>{pokemon.flavorText}</p>  </div></Layout>

Like before:

  • Imported styles are moved to the code fence.
  • className becomes class.
  • <Head> contents are moved into <Layout>.
  • {pokemon.id} values are interpolated the same as before.

However, in addition, now:

Move Next getStaticPaths to Astro

Astro supports a function called getStaticPaths to generate dynamic paths, similar to Next.

Given a Next page:

// pages/pokemon/[name].jsexport const getStaticPaths = async () => {  const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")  const resJson = await res.json();  const pokemons = resJson.results;  return {    paths: pokemons.map(({ name }) => ({      params: { name },    }))  }}

Migrate the getStaticPaths method to Astro by removing the paths route prefix and returning an array:

---// src/pages/pokemon/[name].astroimport styles from '../../styles/pokemon-entry.module.css';export const getStaticPaths = async () => {  const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")  const resJson = await res.json();  const pokemons = resJson.results;  return pokemons.map(({ name }) => ({      params: { name },    }))}---<Layout title={`Pokedex: ${pokemon.name}`}>  <button onclick="history.go(-1)" class={styles.backBtn} aria-label="Go back"></button>  <img class={styles.pokeImage} src={pokemon.image} alt={`${pokemon.name} picture`} />  <div class={styles.infoContainer}>    <h1 class={styles.header}>No. {pokemon.id}: {pokemon.name}</h1>    <table class={styles.pokeInfo}>      <tbody>        <tr>          <th>Types</th>          <td>{pokemon.types}</td>        </tr>        <tr>          <th>Height</th>          <td>{pokemon.height}</td>        </tr>        <tr>          <th>Weight</th>          <td>{pokemon.weight}</td>        </tr>      </tbody>    </table>    <p class={styles.flavor}>{pokemon.flavorText}</p>  </div></Layout>

Then, similar to the previous page, migrate the getStaticProps method to non-function-wrapped code in the Astro page's code fence.

Given the Next page logic:

// pages/pokemon/[name].jsfunction capitalize(str) {  return str.charAt(0).toUpperCase() + str.slice(1);}export const getStaticProps = async (context) => {  const { name } = context.params  const [pokemon, species] = await Promise.all([    fetch(`https://pokeapi.co/api/v2/pokemon/${name}`).then(res => res.json()),    fetch(`https://pokeapi.co/api/v2/pokemon-species/${name}`).then(res => res.json())  ])  return {    props: {      pokemon: {        id: pokemon.id,        image: pokemon.sprites.front_default,        name: capitalize(pokemon.name),        height: pokemon.height,        weight: pokemon.weight,        flavorText: species.flavor_text_entries[0].flavor_text,        types: pokemon.types.map(({ type }) => type.name).join(', ')      },    },  }}

Migrate this to the Astro page's code fence:

Use Astro.props to access the params returned from the getStaticPaths function

---// src/pages/pokemon/[name].astroimport styles from '../../styles/pokemon-entry.module.css';export const getStaticPaths = async () => {  const res = await fetch("https://pokeapi.co/api/v2/pokemon?limit=151")  const resJson = await res.json();  const pokemons = resJson.results;  return pokemons.map(({ name }) => ({      params: { name },    }))}function capitalize(str) {  return str.charAt(0).toUpperCase() + str.slice(1);}const { name } = Astro.props;const [pokemonData, species] = await Promise.all([    fetch(`https://pokeapi.co/api/v2/pokemon/${name}`).then(res => res.json()),    fetch(`https://pokeapi.co/api/v2/pokemon-species/${name}`).then(res => res.json())])const pokemon = {    id: pokemonData.id,    image: pokemonData.sprites.front_default,    name: capitalize(pokemonData.name),    height: pokemonData.height,    weight: pokemonData.weight,    flavorText: species.flavor_text_entries[0].flavor_text,    types: pokemonData.types.map(({ type }) => type.name).join(', ')};---<Layout title={`Pokedex: ${pokemon.name}`}>  <button onclick="history.go(-1)" class={styles.backBtn} aria-label="Go back"></button>  <img class={styles.pokeImage} src={pokemon.image} alt={`${pokemon.name} picture`} />  <div class={styles.infoContainer}>    <h1 class={styles.header}>No. {pokemon.id}: {pokemon.name}</h1>    <table class={styles.pokeInfo}>      <tbody>        <tr>          <th>Types</th>          <td>{pokemon.types}</td>        </tr>        <tr>          <th>Height</th>          <td>{pokemon.height}</td>        </tr>        <tr>          <th>Weight</th>          <td>{pokemon.weight}</td>        </tr>      </tbody>    </table>    <p class={styles.flavor}>{pokemon.flavorText}</p>  </div></Layout>

You have now fully migrated a Pokédex application from Next to Astro.

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