printRangeTest.js

const unique = list => list.filter((value, index, list) => list.indexOf(value) === index);

const sortNumber = (a, b) => a - b;

const expandBlock = (accum, block) => {
  if (block.indexOf('-') === -1) {
    accum.push(parseInt(block));
    return accum;
  }


  const intervals = block.split('-').map(i => parseInt(i)).sort(sortNumber);

  for (var i = intervals[0]; i <= intervals[intervals.length - 1]; i++) {
      accum.push(i)
  }

  return accum;
}

const input = "3 , 7 - 10,4,6, 12-12,  1";

const cleanInput = input.replace(/ /g, "");

const matchPattern = /^((([1-9]\d*)|([1-9]\d*-[1-9]\d*))+,)+(([1-9]\d*)|([1-9]\d*-[1-9]\d*))+$|^[1-9]\d*$|^[1-9]\d*-[1-9]\d*$/;

if (!matchPattern.test(cleanInput)) {
  throw new Error('The input has an invalid format');
}

const blocks = cleanInput.split(',');

const numbers = blocks.reduce(expandBlock, []);

const output = unique(numbers).sort(sortNumber).join(',');

console.log(output);