Incremental builds with data in Astro

Introduction

Incremental builds with data let your website update only the parts that changed. This saves time and makes your site faster to build and load.

When your site has many pages but only some data changes often.

When you want faster updates without rebuilding the whole site.

When you fetch data from APIs or databases and want to keep content fresh.

When you want to save server resources during builds.

When you want to improve developer experience by reducing wait times.

Syntax

Astro

export async function getStaticPaths() {
  const data = await fetchData()
  return data.map(item => ({ params: { id: item.id } }))
}

export async function getStaticProps({ params }) {
  const itemData = await fetchDataById(params.id)
  return { props: { itemData } }
}

getStaticPaths tells Astro which pages to build based on your data.

getStaticProps fetches data for each page during build time.

Examples

This example builds pages only for ids 1 and 2 with simple messages.

Astro

export async function getStaticPaths() {
  return [
    { params: { id: '1' } },
    { params: { id: '2' } }
  ]
}

export async function getStaticProps({ params }) {
  return { props: { message: `Page for id ${params.id}` } }
}

This example fetches blog posts from an API and builds pages for each post slug.

Astro

export async function getStaticPaths() {
  const posts = await fetch('https://api.example.com/posts').then(res => res.json())
  return posts.map(post => ({ params: { slug: post.slug } }))
}

export async function getStaticProps({ params }) {
  const post = await fetch(`https://api.example.com/posts/${params.slug}`).then(res => res.json())
  return { props: { post } }
}

Sample Program

This Astro component builds two pages: one for id 'a' and one for 'b'. Each page shows its own title and content. Only these pages are built, saving time.

Astro

---
export async function getStaticPaths() {
  return [
    { params: { id: 'a' } },
    { params: { id: 'b' } }
  ]
}

export async function getStaticProps({ params }) {
  const data = {
    a: { title: 'Page A', content: 'Content for A' },
    b: { title: 'Page B', content: 'Content for B' }
  }
  return { props: { page: data[params.id] } }
}
---
<html lang="en">
  <head><title>{page.title}</title></head>
  <body>
    <h1>{page.title}</h1>
    <p>{page.content}</p>
  </body>
</html>

Important Notes

Incremental builds only rebuild pages with changed data, making builds faster.

Use getStaticPaths to control which pages get built.

Make sure your data fetching in getStaticProps is fast and reliable.

Summary

Incremental builds update only needed pages, saving time.

Use getStaticPaths and getStaticProps to fetch data for pages.

This approach improves site speed and developer experience.

Practice

1. What is the main benefit of using incremental builds in Astro projects?

easy

A. Only pages with changed data are rebuilt, saving time

B. All pages are rebuilt every time for consistency

C. It disables data fetching during build

D. It automatically deploys the site to a server

Solution

1. Step 1: Understand incremental build purpose

   Incremental builds focus on rebuilding only what changed, not the whole site.

2. Step 2: Identify the benefit in context

   This saves build time and speeds up development and deployment.

3. Final Answer:

   Only pages with changed data are rebuilt, saving time -> Option A

4. Quick Check:

   Incremental builds = rebuild changed pages only [OK]

Hint: Incremental means update only changed parts [OK]

Common Mistakes:

• Thinking all pages rebuild every time
• Confusing incremental builds with disabling data fetching
• Assuming it automatically deploys the site

2. Which Astro function is used to specify which pages should be built incrementally with data?

easy

A. useEffect

B. getServerSideProps

C. renderToString

D. getStaticPaths

Solution

1. Step 1: Recall Astro data fetching functions

   Astro uses getStaticPaths to define dynamic routes for static generation.

2. Step 2: Match function to incremental build role

   getStaticPaths tells Astro which pages to build incrementally with data.

3. Final Answer:

   getStaticPaths -> Option D

4. Quick Check:

   Page list for incremental build = getStaticPaths [OK]

Hint: Use getStaticPaths to list pages for static build [OK]

Common Mistakes:

• Confusing getStaticPaths with getServerSideProps
• Using React hooks like useEffect in Astro build functions
• Thinking renderToString controls incremental builds

3. Given this Astro code snippet, what will be the output for the page paths?

export async function getStaticPaths() {
  return [
    { params: { id: '1' } },
    { params: { id: '2' } }
  ];
}

medium

A. No pages will be built because return type is wrong

B. Only page /1 will be built

C. Pages for /1 and /2 will be built incrementally

D. Pages for /id/1 and /id/2 will be built

Solution

1. Step 1: Analyze getStaticPaths return value

   The function returns an array with params objects containing id '1' and '2'.

2. Step 2: Understand path generation

   Astro uses these params to build pages at /1 and /2 paths incrementally.

3. Final Answer:

   Pages for /1 and /2 will be built incrementally -> Option C

4. Quick Check:

   Params id '1' and '2' create /1 and /2 pages [OK]

Hint: Params define page paths directly [OK]

Common Mistakes:

• Assuming only first param builds a page
• Thinking return type must be an object, not array
• Confusing path format with nested folders

4. Identify the error in this Astro incremental build code snippet:

export async function getStaticPaths() {
  return {
    params: [
      { id: 'a' },
      { id: 'b' }
    ]
  };
}

medium

A. getStaticPaths must return an array, not an object

B. Params should be a string, not an array

C. Function must be synchronous, not async

D. Return value should be a function, not an object

Solution

1. Step 1: Check getStaticPaths return type

   Astro expects getStaticPaths to return an array of params objects, not an object wrapping an array.

2. Step 2: Identify correct return structure

   The code incorrectly returns an object with params array instead of just the array.

3. Final Answer:

   getStaticPaths must return an array, not an object -> Option A

4. Quick Check:

   Return type must be array for getStaticPaths [OK]

Hint: Return array directly from getStaticPaths [OK]

Common Mistakes:

• Wrapping params array inside an object
• Making function synchronous when async is allowed
• Returning a function instead of data

5. You want to build a blog with incremental builds in Astro. You fetch posts from an API and want only new or updated posts to rebuild. Which approach correctly implements this?

hard

A. Use getStaticProps only once to fetch all posts and build all pages at once

B. Use getStaticPaths to list all post IDs, then getStaticProps to fetch data for each ID

C. Use client-side fetching only, no static generation

D. Manually rebuild the entire site on every post update

Solution

1. Step 1: Understand incremental build with data fetching

   Incremental builds require listing pages (post IDs) with getStaticPaths and fetching data per page with getStaticProps.

2. Step 2: Match approach to requirement

   Use getStaticPaths to list all post IDs, then getStaticProps to fetch data for each ID uses getStaticPaths to specify posts and getStaticProps to fetch each post's data, enabling incremental rebuilds.

3. Final Answer:

   Use getStaticPaths to list all post IDs, then getStaticProps to fetch data for each ID -> Option B

4. Quick Check:

   Incremental builds = getStaticPaths + getStaticProps [OK]

Hint: List pages then fetch data per page for incremental builds [OK]

Common Mistakes:

• Fetching all posts at once disables incremental builds
• Relying only on client-side fetching loses static benefits
• Rebuilding entire site wastes time and defeats incremental purpose