chrono.js

function timestamp (times) {
  var intervals = {
    h: 60 * 60 * 1000,
    m: 60 * 1000,
    s: 1000
  };

  return times.reduce(function(memo, c) {
    if (c.match(/[hms]/)) {
      memo[memo.length - 1].i = c;
      memo.push({ s : '' });
    } else if (c.match(/[0-9]/)) {
      memo[memo.length - 1].s += c;
    } else {
      throw new Error('Bad chunk found');
    }
    return memo;
  }, [{ s: '' }]).filter(function(chunk) {
    return chunk.s;
  }).reduce(function(memo, chunk) {
    return memo + Number(chunk.s) * intervals[chunk.i];
  }, 0);
}

console.log(timestamp('01h2m5s'.split('')));