Multiple Pages

webpack-plugin-serve - A Development Server in a webpack Plugin - Interview with Andrew Powell

Even though webpack is often used for bundling single page applications, it's possible to use it with multiple separate pages as well. The idea is similar to the way you generated multiple output files in the Targets chapter. This time, however, you have to generate separate pages. That's achievable through HtmlWebpackPlugin and a bit of configuration.

Possible Approaches#

When generating multiple pages with webpack, you have a couple of possibilities:

  • Go through the multi-compiler mode and return an array of configurations. The approach would work as long as the pages are separate and there is a minimal need for sharing code across them. The benefit of this approach is that you can process it through parallel-webpack to improve build performance.
  • Set up a single configuration and extract the commonalities. The way you do this can differ depending on how you chunk it up.
  • If you follow the idea of Progressive Web Applications (PWA), you can end up with either an app shell or a page shell and load portions of the application as it's used.

In practice, you have more dimensions. For example, you have to generate i18n variants for pages. These ideas grow on top of the basic approaches.

Generating Multiple Pages#

To generate multiple separate pages, they should be initialized somehow. You should also be able to return a configuration for each page, so webpack picks them up and process them through the multi-compiler mode.

Abstracting Pages#

To initialize a page, it should receive page title, output path, and an optional template at least. Each page should receive optional output path and a template for customization. The idea can be modeled as a configuration part:

webpack.parts.js

...
const HtmlWebpackPlugin = require("html-webpack-plugin");

exports.page = ({
  path = "",
  template = require.resolve(
    "html-webpack-plugin/default_index.ejs"
  ),
  title,
} = {}) => ({
  plugins: [
    new HtmlWebpackPlugin({
      filename: `${path && path + "/"}index.html`,
      template,
      title,
    }),
  ],
});

Integrating to Configuration#

To incorporate the idea into the configuration, the way it's composed has to change. Also, a page definition is required. To get started, let's reuse the same JavaScript logic for each page for now:

webpack.config.js

...
const HtmlWebpackPlugin = require("html-webpack-plugin");
... const commonConfig = merge([
{ plugins: [ new HtmlWebpackPlugin({ title: "Webpack demo", }), ], },
... ]); ... module.exports = mode => {
if (mode === "production") { return merge(commonConfig, productionConfig, { mode }); } return merge(commonConfig, developmentConfig, { mode });
const pages = [ parts.page({ title: "Webpack demo" }), parts.page({ title: "Another demo", path: "another" }), ]; const config = mode === "production" ? productionConfig : developmentConfig; return pages.map(page => merge(commonConfig, config, page, { mode }) );
};

After this change you should have two pages in the application: / and /another. It should be possible to navigate to both while seeing the same output.

Injecting Different Script per Page#

The question is, how to inject a different script per each page. In the current configuration, the same entry is shared by both. To solve the problem, you should move entry configuration to lower level and manage it per page. To have a script to test with, set up another entry point:

src/another.js

import "./main.css";
import component from "./component";

const demoComponent = component("Another");

document.body.appendChild(demoComponent);

The file could go to a directory of its own. Here the existing code is reused to get something to show up. Webpack configuration has to point to this file:

webpack.config.js

...

const commonConfig = merge([
{ output: { // Needed for code splitting to work in nested paths publicPath: "/", }, },
... ]); ... module.exports = mode => {
const pages = [ parts.page({ title: "Webpack demo" }), parts.page({ title: "Another demo", path: "another" }), ];
const pages = [ parts.page({ title: "Webpack demo", entry: { app: PATHS.app, }, }), parts.page({ title: "Another demo", path: "another", entry: { another: path.join(PATHS.app, "another.js"), }, }), ];
const config = mode === "production" ? productionConfig : developmentConfig; return pages.map(page => merge(commonConfig, config, page, { mode }) ); };

The tweak also requires a change at the related part so that entry gets included in the configuration:

webpack.parts.js

exports.page = (
  {
    path = "",
    template = require.resolve(
      "html-webpack-plugin/default_index.ejs"
    ),
    title,
entry,
} = {} ) => ({
entry,
plugins: [ new HtmlWebpackPlugin({ filename: `${path && path + "/"}index.html`, title, }), ], });

After these changes /another should show something familiar:

Another page shows up
Another page shows up

Pros and Cons#

If you build the application (npm run build), you should find another/index.html. Based on the generated code, you can make the following observations:

  • It's clear how to add more pages to the setup.
  • The generated assets are directly below the build root. The pages are an exception as those are handled by HtmlWebpackPlugin, but they still point to the assets below the root. It would be possible to add more abstraction in the form of webpack.page.js and manage the paths by exposing a function that accepts page configuration.
  • Records should be written separately per each page in files of their own. Currently, the configuration that writes the last wins. The above solution would allow solving this.
  • Processes like linting and cleaning run twice now. The Targets chapter discussed potential solutions to that problem.

The approach can be pushed in another direction by dropping the multi-compiler mode. Even though it's slower to process this kind of build, it enables code sharing and the implementation of shells. The first step towards a shell setup is to rework the configuration so that it picks up the code shared between the pages.

Generating Multiple Pages While Sharing Code#

The current configuration shares code by coincidence already due to the usage patterns. Only a small part of the code differs, and as a result, only the page manifests, and the bundles mapping to their entries differ.

In a more complicated application, you should apply techniques covered in the Bundle Splitting chapter across the pages. Dropping the multi-compiler mode can be worthwhile then.

Adjusting Configuration#

Adjustment is needed to share code between the pages. Most of the code can remain the same. The way you expose it to webpack has to change so that it receives a single configuration object. As HtmlWebpackPlugin picks up all chunks by default, you have to adjust it to pick up only the chunks that are related to each page:

webpack.config.js

...

module.exports = mode => {
  const pages = [
    parts.page({
      title: "Webpack demo",
      entry: {
        app: PATHS.app,
      },
chunks: ["app", "manifest", "vendors~app"],
}), parts.page({ title: "Another demo", path: "another", entry: { another: path.join(PATHS.app, "another.js"), },
chunks: ["another", "manifest", "vendors~app"],
}), ]; const config = mode === "production" ? productionConfig : developmentConfig;
return pages.map(page => merge(commonConfig, config, page, { mode }) );
return merge([commonConfig, config, { mode }].concat(pages));
};

The page-specific configuration requires a small tweak as well:

webpack.parts.js

exports.page = (
  {
    path = "",
    template = require.resolve(
      "html-webpack-plugin/default_index.ejs"
    ),
    title,
    entry,
chunks,
} = {} ) => ({ entry, plugins: [ new HtmlWebpackPlugin({
chunks,
... }), ], });

If you generate a build (npm run build), you should notice that something is different compared to the first multiple page build. Instead of two manifest files, there's only one. Because of the new setup, the manifest contains references to all of the bundles that were generated. In turn, the entry specific files point to different parts of the manifest and the manifest runs different code depending on the entry. Multiple separate manifests are not therefore needed.

Pros and Cons#

Compared to the earlier approach, something was gained, but also lost:

  • Given the configuration isn't in the multi-compiler form anymore, processing can be slower.
  • Plugins such as CleanWebpackPlugin don't work without additional consideration now.
  • Instead of multiple manifests, only one remains. The result is not a problem, though, as the entries use it differently based on their setup.

Progressive Web Applications#

If you push the idea further by combining it with code splitting and smart routing, you'll end up with the idea of Progressive Web Applications (PWA). webpack-pwa example illustrates how to implement the approach using webpack either through an app shell or a page shell.

App shell is loaded initially, and it manages the whole application including its routing. Page shells are more granular, and more are loaded as the application is used. The total size of the application is larger in this case. Conversely, you can load initial content faster.

PWA combines well with plugins like offline-plugin and sw-precache-webpack-plugin. Using Service Workers and improves the offline experience.

Twitter and Tinder case studies illustrate how the PWA approach can improve platforms.

Conclusion#

Webpack allows you to manage multiple page setups. The PWA approach allows the application to be loaded as it's used and webpack allows implementing it.

To recap:

  • Webpack can be used to generate separate pages either through its multi-compiler mode or by including all the page configuration into one.
  • The multi-compiler configuration can run in parallel using external solutions, but it's harder to apply techniques such as bundle splitting against it.
  • A multi-page setup can lead to a Progressive Web Application. In this case, you use various webpack techniques to come up with an application that is fast to load and that fetches functionality as required. Both two flavors of this technique have their own merits.

You'll learn to implement Server Side Rendering in the next chapter.

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