polybius.fyi/reveal.js/node_modules/underscore.string/strLeftBack.js

var makeString = require('./helper/makeString');

module.exports = function strLeftBack(str, sep) {
  str = makeString(str);
  sep = makeString(sep);
  var pos = str.lastIndexOf(sep);
  return~ pos ? str.slice(0, pos) : str;
};