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Quick Tip: Inline Minified JavaScript

Originally posted on The Simplest Web Site That Could Possible Work Well on

This tip works great if you have small JS utilities that you’d like to have in your <head>. For example, this works great with the Filament Group loadJS or loadCSS utilities.

Installation Jump to heading

npm install terser to make the terser minifier available in your project.

Configuration Jump to heading

Add the following jsmin filter to your Eleventy Config file:

const { minify } = require("terser");
eleventyConfig.addNunjucksAsyncFilter("jsmin", async function (code, callback) {
try {
const minified = await minify(code);
callback(null, minified.code);
} catch (err) {
console.error("Terser error: ", err);
// Fail gracefully.
callback(null, code);

Create your JavaScript File Jump to heading

Add a sample JavaScript file to your _includes directory. Let’s call it sample.js.

// Hi

Capture and Minify Jump to heading

Capture the JavaScript into a variable and run it through the filter (this sample is using Nunjucks syntax)

<!-- capture the JS content as a Nunjucks variable -->
{% set js %} {% include "sample.js" %} {% endset %}
<!-- feed it through our jsmin filter to minify -->
js | jsmin | safe;

Warning about Content Security Policy Jump to heading

If you are using a Content Security Policy on your website, make sure the script-src directive allows 'unsafe-inline'. Otherwise, your inline Javascript will not load.