Sampling uniformly

gistfile1.js

function randomSeq(begin, end, number) {
  var i = 0;
  var range = end - begin;
  var exchanged = {};
  var seq = [];
  while (i < number) {
    const v = i + Math.floor(Math.random() * (range - i));
    if (exchanged[v] !== undefined) {
      seq.push(begin + exchanged[v]);
    } else {
      seq.push(begin + v);
    }

    if (exchanged[i] !== undefined) {
      exchanged[v] = exchanged[i];
    } else {
      exchanged[v] = i;
    }

    ++i;
  }

  return seq;
}