GenerateStaticParams for static paths in NextJS - Step-by-Step Execution

Concept Flow - GenerateStaticParams for static paths

Define generateStaticParams function

↓

Fetch or define list of params

↓

Return array of params objects

↓

Next.js uses params to build static pages

↓

Static pages generated at build time

↓

Pages served fast without server calls

The generateStaticParams function provides Next.js with all the dynamic route parameters it needs to pre-build static pages at build time.

Execution Sample

NextJS

export async function generateStaticParams() {
  return [
    { slug: 'post-1' },
    { slug: 'post-2' }
  ];
}

This function returns an array of objects with slugs, telling Next.js which pages to build statically.

Execution Table

Step	Action	Data/Params	Result
1	Call generateStaticParams	No input	Function starts
2	Return array of params	[{ slug: 'post-1' }, { slug: 'post-2' }]	Next.js receives params
3	Next.js builds static pages	Uses each slug	Pages /post-1 and /post-2 generated
4	Serve pages	User requests /post-1 or /post-2	Page served instantly from static files

💡 All static paths generated; no more params to process

Variable Tracker

Variable	Start	After Return	Final
params	undefined	[{ slug: 'post-1' }, { slug: 'post-2' }]	[{ slug: 'post-1' }, { slug: 'post-2' }]

Key Moments - 2 Insights

Why do we return an array of objects from generateStaticParams?

Because Next.js needs a list of all dynamic route parameters to pre-build each page at build time, as shown in execution_table step 2.

What happens if generateStaticParams returns an empty array?

No static pages for dynamic routes are generated, so those pages won't exist unless fallback is used, as implied by the absence of params in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what does generateStaticParams return at step 2?

A A single object {slug:'post-1'}

B An empty array []

C [{ slug: 'post-1' }, { slug: 'post-2' }]

D Undefined

💡 Hint

Check the 'Data/Params' column at step 2 in execution_table

At which step does Next.js build the static pages?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column describing building pages in execution_table

If we add {slug:'post-3'} to the returned array, what changes in the execution_table?

A Step 4 serves post-3 page only

B Step 2 data includes post-3 and Step 3 builds /post-3 page

C No change, only post-1 and post-2 are built

D Function fails to return

💡 Hint

Adding params affects the returned array and pages built as shown in steps 2 and 3

Concept Snapshot

generateStaticParams is an async function
Returns array of params objects for dynamic routes
Next.js uses these params to pre-build static pages
Pages are generated at build time for fast loading
No server needed to serve these pages
Useful for static site generation with dynamic paths

Full Transcript

The generateStaticParams function in Next.js is used to tell the framework which dynamic routes to pre-build as static pages. When called, it returns an array of objects, each representing parameters for a dynamic route, like slugs for blog posts. Next.js uses this list during the build process to generate static HTML pages for each route. This means when users visit these pages, they load instantly without server delays. If the array is empty, no static pages are generated for those routes. Adding more params adds more static pages. This process improves performance and SEO by serving pre-built pages.

Practice

1. What is the main purpose of generateStaticParams in Next.js?

easy

A. To tell Next.js which dynamic routes to pre-render at build time

B. To fetch data on every user request

C. To handle client-side navigation between pages

D. To define API routes in Next.js

Solution

1. Step 1: Understand the role of generateStaticParams

   This function is used to specify dynamic route parameters for static generation.

2. Step 2: Compare with other Next.js features

   Unlike client-side navigation or API routes, generateStaticParams runs at build time to pre-build pages.

3. Final Answer:

   To tell Next.js which dynamic routes to pre-render at build time -> Option A

4. Quick Check:

   generateStaticParams = pre-render dynamic routes [OK]

Hint: Remember: generateStaticParams runs at build time for static pages [OK]

Common Mistakes:

• Confusing generateStaticParams with client-side data fetching
• Thinking it runs on every request
• Mixing it up with API route definitions

2. Which of the following is the correct syntax for generateStaticParams in a Next.js dynamic route file?

easy

A. export function generateStaticParams() { return ['1', '2']; }

B. export async function generateStaticParams() { return [{ id: '1' }, { id: '2' }]; }

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

D. export default function generateStaticParams() { return { paths: ['1', '2'] }; }

Solution

1. Step 1: Recall the correct return format

   generateStaticParams returns an array of objects with route parameters as keys.

2. Step 2: Check syntax correctness

   export async function generateStaticParams() { return [{ id: '1' }, { id: '2' }]; } correctly exports an async function returning [{ id: '1' }, { id: '2' }]. Others have wrong return types or use getStaticPaths.

3. Final Answer:

   export async function generateStaticParams() { return [{ id: '1' }, { id: '2' }]; } -> Option B

4. Quick Check:

   Return array of param objects = export async function generateStaticParams() { return [{ id: '1' }, { id: '2' }]; } [OK]

Hint: generateStaticParams returns array of objects with params keys [OK]

Common Mistakes:

• Using getStaticPaths instead of generateStaticParams
• Returning array of strings instead of objects
• Not exporting the function properly

3. Given this generateStaticParams function, what static paths will Next.js generate?

export async function generateStaticParams() {
  return [
    { slug: 'home' },
    { slug: 'about' },
    { slug: 'contact' }
  ];
}

medium

A. /home, /about, /contact

B. /slug/home, /slug/about, /slug/contact

C. /, /about, /contact

D. /home, /about, /contact, /blog

Solution

1. Step 1: Understand the returned params

   The function returns an array with slug keys: 'home', 'about', 'contact'.

2. Step 2: Map params to URLs

   Next.js uses these slugs as dynamic route parts, so paths are /home, /about, /contact.

3. Final Answer:

   /home, /about, /contact -> Option A

4. Quick Check:

   Params slug values = generated paths [OK]

Hint: Params keys map directly to URL segments in static paths [OK]

Common Mistakes:

• Adding extra path segments like /slug/
• Assuming root path / is included automatically
• Including paths not returned by generateStaticParams

4. Identify the error in this generateStaticParams function:

export async function generateStaticParams() {
  return [
    { id: 1 },
    { id: 2 },
    { id: 3 }
  ]
}

medium

A. There is no error; this is correct syntax

B. The function must return an object, not an array

C. The function must be named getStaticPaths instead

D. The id values should be strings, not numbers

Solution

1. Step 1: Check parameter types

   Route parameters in Next.js must be strings because URLs are strings.

2. Step 2: Identify type mismatch

   Here, id values are numbers (1, 2, 3), which can cause build errors or unexpected behavior.

3. Final Answer:

   The id values should be strings, not numbers -> Option D

4. Quick Check:

   Route params must be strings [OK]

Hint: Always use strings for route parameters in generateStaticParams [OK]

Common Mistakes:

• Returning numbers instead of strings for params
• Confusing generateStaticParams with getStaticPaths
• Returning object instead of array

5. You want to statically generate blog post pages with slugs from an API. Which generateStaticParams implementation correctly fetches slugs and returns them for static generation?

async function fetchSlugs() {
  return ['post-1', 'post-2', 'post-3'];
}

Choose the correct code:

hard

A. export async function generateStaticParams() {
const slugs = await fetchSlugs();
return slugs;
}

B. export async function generateStaticParams() {
const slugs = await fetchSlugs();
return { paths: slugs };
}

C. export async function generateStaticParams() {
const slugs = await fetchSlugs();
return slugs.map(slug => ({ slug }));
}

D. export async function generateStaticParams() {
const slugs = await fetchSlugs();
return slugs.map(slug => ({ params: { slug } }));
}

Solution

1. Step 1: Understand expected return format

   generateStaticParams expects an array of objects with route params keys directly, e.g. [{ slug: 'post-1' }].

2. Step 2: Analyze each option

   export async function generateStaticParams() { const slugs = await fetchSlugs(); return slugs.map(slug => ({ slug })); } returns slugs mapped to objects with slug keys correctly. export async function generateStaticParams() { const slugs = await fetchSlugs(); return { paths: slugs }; } returns an object, not array. export async function generateStaticParams() { const slugs = await fetchSlugs(); return slugs; } returns array of strings, not objects. export async function generateStaticParams() { const slugs = await fetchSlugs(); return slugs.map(slug => ({ params: { slug } })); } adds extra params key, which is incorrect for generateStaticParams.

3. Final Answer:

   export async function generateStaticParams() { const slugs = await fetchSlugs(); return slugs.map(slug => ({ slug })); } -> Option C

4. Quick Check:

   Return array of param objects without extra nesting [OK]

Hint: Map slugs to objects with keys matching route params [OK]

Common Mistakes:

• Returning object with paths key instead of array
• Returning array of strings instead of objects
• Adding extra nesting like { params: { slug } }