prerender-node

3.8.3 verified Sat Apr 25 auth: no javascript

Express middleware for serving prerendered JavaScript-rendered pages to crawlers (Google, Facebook, Twitter, Bing) to improve SEO for Angular, React, Vue, and other JS frameworks. Current stable version: 3.8.3. Released as needed, maintained actively. Key differentiator: integrates with Prerender.io cloud service or self-hosted prerender server, supports whitelist/blacklist, beforeRender/afterRender hooks. Compared to alternatives like puppeteer-based solutions, it offloads rendering to an external service, reducing server load.

Common errors

error Cannot find module 'prerender-node' ↓

cause Package not installed or missing from package.json.

fix

Run 'npm install prerender-node --save' to install the package.

error prerender-node: no token set, using default (free) service ↓

cause You did not set a prerenderToken, so the middleware falls back to the free public service (limited).

fix

Set your token via .set('prerenderToken', 'YOUR_TOKEN') or set the PRERENDER_TOKEN environment variable.

error prerender-node: beforeRender must return a string or a promise that resolves to a string ↓

cause The beforeRender callback returned something other than a string or Promise<string>.

fix

Ensure beforeRender returns a string (e.g., cache key) or a Promise resolving to a string.

Warnings

gotcha Cannot use import (ESM) with prerender-node; it's CommonJS only. ↓

fix Use const prerender = require('prerender-node');

gotcha Whitelist/blacklist methods are named 'whitelisted' and 'blacklisted' (with 'ed'), not 'whitelist'/'blacklist'. ↓

fix Use .whitelisted('/path') and .blacklisted('/path') correctly.

gotcha Local development requires running a local prerender server (https://github.com/prerender/prerender) because the cloud service cannot access localhost. ↓

fix Clone and run the prerender server locally, then set PRERENDER_SERVICE_URL environment variable to point to it.

deprecated The 'set' method with 'prerenderToken' is the only supported way to configure the token; old methods like 'setPrerenderToken' are removed. ↓

fix Use .set('prerenderToken', 'YOUR_TOKEN')

gotcha The default user agent list may not cover all crawlers; custom crawlers can be added via .crawlerUserAgent() method. ↓

fix Use prerender.crawlerUserAgent('MyCrawler') to add custom user agents.

Install

npm install prerender-node

yarn add prerender-node

pnpm add prerender-node

Imports

default

wrong

import prerender from 'prerender-node';

correct

const prerender = require('prerender-node'); app.use(prerender);

This package is CommonJS only; does not support ESM imports. Use require().

default with token
```
app.use(require('prerender-node').set('prerenderToken', 'YOUR_TOKEN'));
```
To use the Prerender.io cloud service, you must set the 'prerenderToken' via .set(). Not needed if self-hosting.
whitelisted
wrong
```
app.use(require('prerender-node').whitelist('/search'));
```
correct
```
app.use(require('prerender-node').whitelisted('/search'));
```
Method is 'whitelisted' not 'whitelist'. Accepts string or array of paths (regex-compatible).

blacklisted

wrong

app.use(require('prerender-node').blacklist('/admin'));

correct

app.use(require('prerender-node').blacklisted('/admin'));

Method is 'blacklisted' not 'blacklist'. Accepts string or array of paths.

Quickstart

Sets up Express middleware for prerendering: uses token from env or runs without, then serves a simple HTML page.

const express = require('express');
const prerender = require('prerender-node');

const app = express();
const PORT = process.env.PORT || 3000;
const PRERENDER_TOKEN = process.env.PRERENDER_TOKEN ?? '';

if (PRERENDER_TOKEN) {
  app.use(prerender.set('prerenderToken', PRERENDER_TOKEN));
} else {
  app.use(prerender);
}

app.get('/', (req, res) => {
  res.send(`
    <html>
      <head><title>Test</title></head>
      <body>
        <div id="root">Hello World</div>
        <script>document.getElementById('root').innerHTML = 'Prerendered';</script>
      </body>
    </html>
  `);
});

app.listen(PORT, () => console.log(`Server running on port ${PORT}`));