11ty filter to split a string {{content}} into an excerpt (i.e. all stuff before <!--more-->) and the remainder (i.e. stuff after that tag...). Source: https://hawksworx.com

11ty_excerpts.js

/**
 * Split the content into excerpt and remainder
 *
 * @param {String} str
 * @param {String [excerpt | remainder]} section
 *
 * If excerpt or nothing is passed as an argument, we return what was before the split marker.
 * If remainder is passed as an argument, we return the rest of the post
 *
 */
module.exports = function(str, section) {
  var content = new String(str);
  var delimit = "<!--more-->";
  var parts = content.split(delimit);
  var which = section == 'remainder' ? 1 : 0;
  if(parts.length) {
    return parts[which];
  } else {
    return str
  }
}