Eleventy supports Nunjucks globals

Eleventy v1.0.0 (and above) supports Nunjucks globals. This lets you register a global value or function that is available in all Nunjucks templates.

module.exports = (eleventyConfig) {
  // Register two globals, a static value and a function
  eleventyConfig.addNunjucksGlobal("message", "Hello World");
  eleventyConfig.addNunjucksGlobal("greeting", (name) => `Hello ${name}`);
}

Now you can use {{ message }} and {{ greeting('John') }} in your Nunjucks templates.

A more useful example is a global function that generates a unique id. You may need this if you want to connect a label with its input or for aria-labelledby and aria-describedby. Here I use the nanoid package to generate the id:

const { nanoid } = require("nanoid");
module.exports = (eleventyConfig) =>
  eleventyConfig.addNunjucksGlobal("nanoid", () => nanoid());
};

Now you can create a new unique id, assign it to a local variable and use it to connect two HTML elements:

{% set id = nanoid() %}
<article aria-labelledby="{{ id }}">
  <h2 id="{{ id }}">...</h2>
  <p>...</p>
</article>

In the example above we connect the h2 with the article element using aria-labelledby.