leecat.art/_config/filters.js

import { DateTime } from "luxon";

export default function (eleventyConfig) {
	// Return the keys used in an object
	eleventyConfig.addFilter("getKeys", (target) => {
		return Object.keys(target);
	});

	/* Exclude all posts with given URLs from a collection list */
	eleventyConfig.addFilter(
		"excludeFromCollection",
		function (collection = [], urls = [this.ctx.page.url]) {
			return collection.filter((post) => urls.indexOf(post.url) === -1);
		},
	);

	/* Filter a collection by a set of tags, returning any that share one or more tags */
	eleventyConfig.addFilter(
		"filterByTags",
		function (collection = [], ...requiredTags) {
			return collection.filter((post) => {
				return requiredTags.flat().some((tag) => post.data.tags.includes(tag));
			});
		},
	);

	/* Return n elements from a list */
	eleventyConfig.addFilter("head", (collection = [], n) => {
		if (!Array.isArray(collection) || collection.length === 0) {
			return [];
		}
		if (n < 0) {
			return collection.slice(n);
		}

		return collection.slice(0, n);
	});

	/* For <time> elements */
	eleventyConfig.addFilter("htmlDateString", (dateObj) => {
		return DateTime.fromJSDate(dateObj, { zone: "utc" }).toFormat("yyyy-LL-dd");
	});

	/* What it says on the tin */
	eleventyConfig.addFilter("randomize", function (array) {
		// Create a copy of the array to avoid modifying the original
		let shuffledArray = array.slice();

		// Fisher-Yates shuffle algorithm
		for (let i = shuffledArray.length - 1; i > 0; i--) {
			const j = Math.floor(Math.random() * (i + 1));
			[shuffledArray[i], shuffledArray[j]] = [
				shuffledArray[j],
				shuffledArray[i],
			];
		}

		return shuffledArray;
	});

	/* Human-readable dates */
	eleventyConfig.addFilter("readableDate", (dateObj) => {
		return DateTime.fromJSDate(dateObj, { zone: "utc" }).toLocaleString(
			DateTime.DATE_FULL,
		);
	});

	/* Filter out structural tags */
	eleventyConfig.addFilter("removeBasicTags", (tags) => {
		return tags.filter(
			(tag) =>
				[
					"all",
					"posts",
					"gallery",
					"reference",
					"tagPagination",
					"blur",
				].indexOf(tag) === -1,
		);
	});

	/* What it says on the tin */
	eleventyConfig.addFilter("sortAlphabetically", (strings) =>
		(strings || []).sort((b, a) => b.localeCompare(a)),
	);

	/* Remove year from image filenames for OG metadata file path */
	eleventyConfig.addFilter("toOgFilename", (filename) => {
		return filename.split("/")[1];
	});
}