On demand

Plugin to render pages on demand in Deno Deploy

Options See on deno.land

routesPath string

The file path to save the routes

preloadPath string

The file path to save the preloaded modules

extraData function

Extra data to pass to the pages


This plugin allows to render pages on demand. It can be useful in some scenarios:

  • There are pages with dynamic content that must be generated at the request time.
  • The site is too big, with thousands of pages, so the build takes too much time.

Lume can generate pages on demand for these cases.

Note: This plugin only works with Deno Deploy.{.tip}


Import this plugin in your _config.ts file to use it:

import lume from "lume/mod.ts";
import onDemand from "lume/plugins/on_demand.ts";

const site = lume();

site.use(onDemand(/* Options */));

export default site;

How does it work?

1. Mark the ondemand pages

First, you need to configure the pages that must be rendered on demand. This is done by setting the ondemand variable to true. For example, let's say we want to render the home page dynamically:

layout: layout.njk
title: This is a title
ondemand: true

<h1>{{ title }}</h1>

2. The _routes.json file

When the site is built, the pages with the ondemand variable are skipped and a _routes.json file is generated containing a map with the associated page file for each URL, for example:

  "/": "./index.njk"

3. The _preload.ts file

If your source folder contains any file with extensions .ts, .tsx, .js, .jsx or .mjs, the archive _preload.ts is also created. This file is important if your site is hosted on Deno Deploy.

Deno Deploy only can import dynamically files that are statically analyzable in the code. The _preload.ts file contains code that does nothing but Deno Deploy can analyze and prepare to execute on demand. You have more info in the Deno Deploy's Changelog.

4. The serve file

Finally, we have to configure a HTTP server with the onDemand middleware. Create the file serve.ts, that will be used by Deno Deploy with the following code:

import site from "./_config.ts";
import Server from "lume/core/server.ts";
import onDemand from "lume/middlewares/on_demand.ts";
import "./_preload.ts";

const server = new Server({
  port: 8000,
  root: site.dest(),

server.use(onDemand({ site }));


console.log("Listening on http://localhost:8000");

The middleware needs an instance of our site in order to render the pages. We can import it from the _config.ts file. It also automatically loads the _routes.json file in order to know which file needs to be rendered for each URL.

And that's all! The _routes.json file is regenerated automatically by the build to ensure it's up to date with your changes.

Using extra data

If you want to use dynamic data, use the option extraData which accepts a function that must return an object with the extra data to be passed to the page. For example, let's say we want to pass the search parameters of the request's url:

import lume from "lume/mod.ts";
import onDemand from "lume/plugins/on_demand.ts";

  extraData(request: Request) {
    const searchParams = new URL(request.url).searchParams;
    const params = Object.fromEntries(searchParams.entries());

    return {

export default site;

Now, the on-demand pages will have the params key with the search params values. For example, in a Nunjucks page:

layout: layout.njk
ondemand: true
url: /example/

Hello {{ params.name }}

The URL /example/?name=Óscar will return Hello Óscar.

See an example

You can see a live example of a site with two pages generated on demand. And the repository with the source code.