The Vercel adapter handles Static Site Generation (SSG) by processing static file outputs and configuring them for optimal delivery on Vercel’s infrastructure.
Static file handling
The adapter processes static outputs during the build phase:
Static file detection
All static files from the build are collected:await handleStaticOutputs(outputs.staticFiles, {
config,
vercelConfig,
vercelOutputDir,
});
index.ts:73-77 Output processing
Each static file is copied to the Vercel output directory with proper configuration:await Promise.all(
outputs.map(async (output) => {
await fsSema.acquire();
const srcExtension = path.extname(output.filePath);
const isHtml = srcExtension === '.html';
if (isHtml) {
vercelConfig.overrides[
path.posix.join('./', output.pathname + '.html')
] = {
contentType: 'text/html; charset=utf-8',
path: path.posix.join('./', output.pathname),
};
}
const destination = path.join(
vercelOutputDir,
'static',
output.pathname + (isHtml ? '.html' : '')
);
await copy(output.filePath, destination);
})
);
outputs.ts:111-142 Content-Type configuration
HTML files receive special handling to ensure proper content type and clean URLs:
- Files are saved with
.html extension
- Content-Type override set to
text/html; charset=utf-8
- Path override removes
.html from the URL
Public directory handling
Static assets from the public directory are automatically processed:
await handlePublicFiles(
path.join(projectDir, 'public'),
vercelOutputDir,
config
);
index.ts:68-72
The implementation copies public files while respecting the basePath configuration:
const destination = path.join(
vercelOutputDir,
'static',
config.basePath || '',
item
);
outputs.ts:81-86
Static route handling
Static pages are detected during the build process:
for (const output of [
...outputs.appPages,
...outputs.appRoutes,
...outputs.pages,
...outputs.pagesApi,
...outputs.staticFiles,
]) {
if (output.pathname.endsWith('/404')) {
has404Output = true;
}
if (output.pathname.endsWith('/500')) {
has500Output = true;
}
}
index.ts:87-104
404 and 500 pages
The adapter automatically configures custom error pages:
const notFoundPath = hasNotFoundOutput
? '/_not-found'
: has404Output
? '/404'
: '/_error';
index.ts:126-130
The adapter prioritizes App Router’s _not-found page over Pages Router’s 404 page, falling back to _error if neither exists.
Static optimization
HTML files
HTML files receive special optimization through content-type overrides:
vercelConfig.overrides[
path.posix.join('./', output.pathname + '.html')
] = {
contentType: 'text/html; charset=utf-8',
path: path.posix.join('./', output.pathname),
};
- Proper MIME type for HTML content
- Clean URLs without
.html extension
- Optimal browser caching
Location: outputs.ts:123-128
Concurrent processing
Static files are processed concurrently using semaphores for optimal performance:
const fsSema = new Sema(16, { capacity: outputs.length });
await Promise.all(
outputs.map(async (output) => {
await fsSema.acquire();
// ... process file
fsSema.release();
})
);
outputs.ts:109-142
The adapter processes up to 16 files concurrently, balancing performance with system resources.
basePath support
All static files respect the basePath configuration:
const destination = path.join(
vercelOutputDir,
'static',
config.basePath || '',
item
);
Not Found fallback
The adapter creates a fallback file for _next/static 404 responses:
await fs.writeFile(
path.posix.join(
vercelOutputDir,
'static',
config.basePath || '',
'_next/static/not-found.txt'
),
'Not Found'
);
outputs.ts:144-152
This file ensures that missing static assets return appropriate 404 responses instead of falling back to the application.