eleventy.config.collection.js

const path = require("path");

module.exports = function (eleventyConfig) {
	eleventyConfig.addFilter("field", (array, field) => {
		const result = array.map((i) => {
			return i.data[field];
		});
		return result;
	});

	eleventyConfig.addFilter("filter", (array, field, value) => {
		return array.filter((i) => {
			return i.data[field] === value;
		});
	});

	eleventyConfig.addFilter("unique", (array) => {
		return [...new Set(array)];
	});

	eleventyConfig.addFilter("sortByDirectoryPrefix", (array) => {
		const getNumberPrefix = (inputPath) => {
			const dirName = path.basename(path.dirname(inputPath));
			const prefix = dirName.split("-")[0];
			const [beforeDecimal, afterDecimal] = prefix.split(".").map(Number);
			return [beforeDecimal, afterDecimal || 0];
		};
		return array.sort((a, b) => {
			const [aBefore, aAfter] = getNumberPrefix(a.inputPath);
			const [bBefore, bAfter] = getNumberPrefix(b.inputPath);
			if (aBefore === bBefore) {
				return aAfter - bAfter;
			}
			return aBefore - bBefore;
		});
	});

	eleventyConfig.addFilter("sort", (array, key, ascending = true) => {
		if (ascending) {
			return array.sort((a, b) => {
				if (a.data[key] > b.data[key]) {
					return 1;
				}
				return -1;
			});
		} else {
			return array.sort((a, b) => {
				if (a.data[key] > b.data[key]) {
					return -1;
				}
				return 1;
			});
		}
	});
};