parse-pagination.js

const parsePagination = s =>
  s
  .split(',')
  .map(s => {
    if(s.match(/^\d+$/)){
      return parseInt(s);
    }
    if(s.match(/^\d+-\d+$/)){
      s = s.split('-');
      return Array(s[1] - s[0] + 1)
        .fill(0)
        .map((v, i) => i + parseInt(s[0]));
    }
    throw new SyntaxError('Cannot parse string ' + s);
  })
  .reduce((acc, v) => acc.concat(v), []);

parsePagination('1,2,3,5-7,20,22');
// [1,2,3,5,6,7,20,22]