@espcom/esbuild-plugin-inject-preload

This is an esbuild plugin designed to inject links into HTML templates. It processes output files from esbuild, and allows to insert these links into specific placeholders within an HTML file based on a given template and options.

Features

• Supports both ESM and CJS environments
• Works across all platforms (Linux, Windows, etc.)
• Works in watch mode and with any configuration of entryNames, assetNames and publicPath

Installation

To install the plugin, run the following command:

npm install @espcom/esbuild-plugin-inject-preload --save-dev

Usage

To use the plugin, add it to the plugins array in your esbuild configuration.

Example

import { pluginInjectPreload } from '@espcom/esbuild-plugin-inject-preload';

esbuild.build({
  entryPoints: ['src/entry.ts'],
  bundle: true,
  outdir: 'dist', // Required by the plugin
  metafile: true, // Required by the plugin
  plugins: [
    pluginInjectPreload([
      {
        templatePath: path.resolve('dist/template.html'),
        replace: '<!-- FONT_PRELOAD --><!-- /FONT_PRELOAD -->',
        as(filePath) {
          if (filePath.endsWith('.woff2') || filePath.endsWith('.woff')) {
            return `<link as="font" crossorigin="anonymous" href="${filePath}" rel="preload">`;
          }
        },
      },
      {
        templatePath: path.resolve('dist/template.html'),
        replace: '<!-- ENTRY_SCRIPT --><!-- /ENTRY_SCRIPT -->',
        as(filePath) {
          if (/entry([^.]+)?\.js/.test(filePath)) {
            return `<script src="${filePath}" defer=""></script>`;
          }
        },
      },
    ])
  ]
});

So, the resulting HTML file will contain smth. like

<!-- FONT_PRELOAD -->
<link as="font" crossorigin="anonymous" href="dist/Roboto-Regular.woff" rel="preload">
<link as="font" crossorigin="anonymous" href="dist/Roboto-Medium.woff2" rel="preload">
<!-- /FONT_PRELOAD -->
<!-- ENTRY_SCRIPT -->
<script src="dist/entry.js" defer=""></script>
<!-- /ENTRY_SCRIPT -->

Options

The plugin accepts an array of options. Each option object must contain the following properties:

• templatePath (string): Path to the HTML template file where the links should be injected.
• replace (string): The placeholder in the template to be replaced by the links. It must be a closed HTML comment, e.g., <!-- preload-links --><!-- /preload-links -->.
• as (function): A function that takes a file path as an argument and returns the corresponding HTML element as a string.

Important Notes

• The metafile and outdir options in the esbuild configuration must be set for the plugin to function correctly.
• The template file should be present, this plugin does not copy it. So use smth. like esbuild-copy-plugin before this plugin

Alternatives

Currently, there are no alternatives for injecting preloading links. However, there is a plugin called esbuild-plugin-html that allows for injecting entry point scripts. In most cases, using @espcom/esbuild-plugin-inject-preload is sufficient. Nevertheless, the esbuild-plugin-html plugin offers powerful options such as findRelatedCssFiles, findRelatedOutputFiles, and inline, making it a better choice for complex projects. Notably, @espcom/esbuild-plugin-inject-preload is fully compatible with esbuild-plugin-html if placed after it in the plugins list.