---
date: '2023-06-07'
title: 'Optimizing for performance with Eleventy'
draft: false
tags: ['Eleventy', 'development']
image: https://cdn.coryd.dev/blog/page-speed.jpg
---
In the interest of over-engineering my personal site I've gone out of my way to optimize it for performance. It started out fairly quick as it's static, built using [Eleventy](https://www.11ty.dev) and is hosted with Vercel but, beyond the basic setup, I've taken some additional measures to drive the [pagespeed](https://pagespeed.web.dev) scores to `100` across the board.
## Limit client side JavaScript
I use a minimal amount of client-side JavaScript for behavior on my site, namely these blocks from my `base.liquid` template:
```javascript
const isDarkMode = () => localStorage.theme === 'dark' || (!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches);
if (isDarkMode()) {
document.documentElement.classList.add('dark')
} else {
document.documentElement.classList.remove('dark')
}
...
document.getElementById("toggleDarkMode").addEventListener("click", function() {
if (isDarkMode()) {
localStorage.theme = 'light'
document.documentElement.classList.remove('dark')
} else {
localStorage.theme = 'dark'
document.documentElement.classList.add('dark')
}
});
(function() {
const pagination = document.getElementById('pagination');
if (pagination) {
pagination.addEventListener('change', (event) => {
const page = parseInt(event.target.value)
if (page === 1) {
window.location.href = '/'
} else {
window.location.href = `/${
event.target.value - 1
}/`
}
})
}
})()
```
These blocks allow the dark theme to be set based on the user's system preferences or at their discretion, using a button in the navigation. Additionally, the final function enables navigating between pages quickly using the `select` at the bottom of each blog listing page.
Everything is in line and concise without external script references. The lone external script is used for [Vercel's privacy friendly analytics](https://vercel.com/analytics).
## Inline and minify CSS
I use [Tailwind](https://tailwindcss.com) for CSS styles[^1] which is minified at build time:
```bash
ELEVENTY_PRODUCTION=true eleventy && NODE_ENV=production npx tailwindcss -i ./tailwind.css -c ./tailwind.config.js -o _site/assets/styles/tailwind.css --minify
```
The site include's Prism for code syntax highlighting and this is embedded and minified in the `` of each page at build time:
{% raw %}
```liquid
{% capture css %}
{% include "../assets/styles/prism.css" %}
{% endcapture %}
```
{% endraw %}
This is made possible by leveraging CleanCSS in (you guessed it) `.eleventy.js`:
{% raw %}
```javascript
const CleanCSS = require('clean-css')
...
// css filters
eleventyConfig.addFilter('cssmin', (code) => new CleanCSS({}).minify(code).styles)
```
{% endraw %}
## Minify HTML output
Final HTML output for the site is minified when it's built using `@sherby/eleventy-plugin-files-minifier` which, [per the docs](https://www.npmjs.com/package/@sherby/eleventy-plugin-files-minifier):
> This plugin allow you to automatically **minify** files when building with **[Eleventy](https://www.11ty.dev/)**. It currently supports `css`, `html`, `json`, `xml`, `xsl` and `webmanifest` files.
Implementing this in `.eleventy.js` is straightforward:
```javascript
const pluginFilesMinifier = require('@sherby/eleventy-plugin-files-minifier')
...
module.exports = function (eleventyConfig) {
eleventyConfig.addPlugin(pluginFilesMinifier)
...
}
```
## Optimize images
Finally (and this is something that took me longer than it should have to do), we optimize images at build time using `@11ty/eleventy-image`, defining a shortcode in `.eleventy.js` as follows:
{% raw %}
```javascript
// image shortcode
eleventyConfig.addShortcode('image', async function (src, alt, css, sizes, loading) {
let metadata = await Image(src, {
widths: [75, 150, 300, 600],
formats: ['webp'],
urlPath: '/assets/img/cache/',
outputDir: './_site/assets/img/cache/',
})
let imageAttributes = {
class: css,
alt,
sizes,
loading: loading || 'lazy',
decoding: 'async',
}
return Image.generateHTML(metadata, imageAttributes)
})
```
{% endraw %}
This is most impactful on [my now page](https://coryd.dev/now) which is populated with quite a few images and, when used, looks something like this:
{% raw %}
```liquid
{% image artistImg, artistName, 'rounded-lg' %}
```
{% endraw %}
For this page in particular, the images that are rendered above the fold are set to load as `eager` to mitigate performance impacts related to [too much lazy loading](https://web.dev/lcp-lazy-loading/). These images are fetched from caches hosted at Bunny.net when the site is built.
All of these boilerplate steps leave us with a quick to load, accessible and resilient site:
{% image '', 'Pagespeed scores for coryd.dev/now', 'border border-blue-500 dark:border-blue-200 rounded-lg overflow-hidden [&>*]:w-full' %}
[^1]: It's easy, flexible and helps mitigate my lack of an eye for design by providing safe baselines.