lewisdale.dev/config/filters/excerpt.js

module.exports = function (eleventyConfig) {
    eleventyConfig.addFilter('excerpt', (content, limit = 250) => {
        const withoutTags = content.replace(/(<([^>]+)>)/gi, "");

        if (withoutTags.length > limit) {
            return withoutTags.slice(0, limit) + " […]";
        }
        return withoutTags;
    });
}