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JavaScript Data Files

Contents

The following applies to both:

Using JS Data Files

You can export data from a JavaScript file to add data, too. This allows you to execute arbitrary code to fetch data at build time.

export default ["user1", "user2"];
module.exports = ["user1", "user2"];

If you return a function, we’ll use the return value from that function.

export default function () {
	return ["user1", "user2"];
}
module.exports = function () {
	return ["user1", "user2"];
}

We use await on the return value, so you can return a promise and/or use an async function, too. Fetch your data asynchronously at build time!

async function fetchUserData(username) {
	// do some async things
	return username;
}

export default async function () {
	let user1 = await fetchUserData("user1");
	let user2 = await fetchUserData("user2");

	return [user1, user2];
};
async function fetchUserData(username) {
	// do some async things
	return username;
}

module.exports = async function () {
	let user1 = await fetchUserData("user1");
	let user2 = await fetchUserData("user2");

	return [user1, user2];
};

Fetching data from a remote API

You’ll want to use Eleventy’s Fetch plugin to request and cache data from remote APIs. There is another example on Quick Tip #009—Cache Data Requests.

Arguments to Global Data Files

When using a callback function in your JavaScript Data Files, Eleventy will now supply any global data already processed via the Configuration API (eleventyConfig.addGlobalData) as well as the eleventy global variable.

export default function (configData) {
	if (configData.eleventy.env.source === "cli") {
		return "I am on the command line";
	}

	return "I am running programmatically via a script";
}
module.exports = function (configData) {
	if (configData.eleventy.env.source === "cli") {
		return "I am on the command line";
	}

	return "I am running programmatically via a script";
}

Examples

Example: Using GraphQL

This “Hello World” GraphQL example works out of the box with Eleventy:

import { graphql, buildSchema } from "graphql";

// this could also be `async function`
export default function () {
	// if you want to `await` for other things here, use `async function`
	var schema = buildSchema(`type Query {
    hello: String
  }`);

	var root = {
		hello: () => "Hello world async!",
	};

	return graphql(schema, "{ hello }", root);
};
const { graphql, buildSchema } = require("graphql");

// this could also be `async function`
module.exports = function () {
	// if you want to `await` for other things here, use `async function`
	var schema = buildSchema(`type Query {
    hello: String
  }`);

	var root = {
		hello: () => "Hello world async!",
	};

	return graphql(schema, "{ hello }", root);
};

Example: Exposing Environment Variables

You can expose environment variables to your templates by utilizing Node.js’ process.env property. (Related: Eleventy also supplies a few of its own Environment Variables)

Start by creating a Global Data file (*.js inside of your _data directory) and export the environment variables for use in a template:

_data/myProject.js
export default function () {
	return {
		environment: process.env.MY_ENVIRONMENT || "development",
	};
}
module.exports = function () {
	return {
		environment: process.env.MY_ENVIRONMENT || "development",
	};
}

Saving this as myProject.js in your global data directory (by default, this is _data/) gives you access to the myProject.environment variable in your templates.

When MY_ENVIRONMENT is set, the value from myProject.environment will be globally available to be used in your templates. If the variable hasn’t been set, the fallback "development" will be used.

Template Usage

Working from our Inline CSS Quick Tip, we can modify the output to only minify our CSS if we’re building for production:

<style>
{% if myProject.environment == "production" %}
	{{ css | cssmin | safe }}
{% else %}
	{{ css | safe }}
{% endif %}
</style>

Other pages in Using Data: