firefish-archive/config/filters/dates.js

const locale = 'en-GB'; // change this to your locale if you want a different date/time format

module.exports = function (eleventyConfig) {
    eleventyConfig.addFilter('dateDisplay', date => new Date(date).toLocaleDateString(locale, {
        "dateStyle": "short"
      }));
    
      eleventyConfig.addFilter('dateTimeDisplay', date => new Date(date).toLocaleString(locale, {
        'dateStyle': 'short',
        'timeStyle': 'short',
        'hourCycle': 'h12'
      }));

      eleventyConfig.addFilter('toDate', date => new Date(date));
}