Fix: Invalid Value Returned by getStaticPaths in Astro

What Causes This Error?

This error occurs when getStaticPaths() returns something other than an array. The function must return an array of path objects, even if it’s empty.

The Problem

---
// ❌ Returns undefined (no return statement)
export function getStaticPaths() {
  const posts = fetchPosts();
}

// ❌ Returns an object instead of array
export function getStaticPaths() {
  return { params: { slug: 'post-1' } };
}

// ❌ Returns null
export function getStaticPaths() {
  return null;
}

// ❌ Returns a string
export function getStaticPaths() {
  return 'post-1';
}
---

The Fix

Return an Array

---
// ✅ Always return an array
export function getStaticPaths() {
  return [
    { params: { slug: 'post-1' } },
    { params: { slug: 'post-2' } },
  ];
}
---

Empty Array for No Pages

---
// ✅ Empty array is valid
export function getStaticPaths() {
  return [];
}
---

With Async/Await

---
// ✅ Async function returning array
export async function getStaticPaths() {
  const posts = await fetchPosts();
  return posts.map((post) => ({
    params: { slug: post.slug },
  }));
}
---

Common Scenarios

Forgetting Return Statement

---
// ❌ Missing return
export async function getStaticPaths() {
  const posts = await getCollection('blog');
  posts.map((post) => ({
    params: { slug: post.slug },
  }));
}

// ✅ Add return
export async function getStaticPaths() {
  const posts = await getCollection('blog');
  return posts.map((post) => ({
    params: { slug: post.slug },
  }));
}
---

Conditional Returns

---
// ❌ Might return undefined
export async function getStaticPaths() {
  const posts = await fetchPosts();
  if (posts.length > 0) {
    return posts.map((p) => ({ params: { slug: p.slug } }));
  }
  // No return here = undefined
}

// ✅ Always return array
export async function getStaticPaths() {
  const posts = await fetchPosts();
  if (posts.length === 0) {
    return [];
  }
  return posts.map((p) => ({ params: { slug: p.slug } }));
}
---

Single Path Wrapped in Array

---
// ❌ Single object, not array
export function getStaticPaths() {
  return { params: { slug: 'only-post' } };
}

// ✅ Wrap in array
export function getStaticPaths() {
  return [{ params: { slug: 'only-post' } }];
}
---

Using forEach Instead of map

---
// ❌ forEach returns undefined
export function getStaticPaths() {
  const paths = [];
  posts.forEach((post) => {
    paths.push({ params: { slug: post.slug } });
  });
  // Missing return!
}

// ✅ Use map or return the array
export function getStaticPaths() {
  return posts.map((post) => ({
    params: { slug: post.slug },
  }));
}
---

Quick Checklist

• getStaticPaths must return an array
• Include explicit return statement
• Use .map() to transform data into path objects
• Empty array [] is valid for zero pages
• Don’t return single objects, strings, or null