Fisher-Yates法

fisher_yates.js

// http://qiita.com/nyawach/items/108c8e2551c26674f57b
function combination(n, m) {

  var list = [];
  m = (m == null) ? n : m;

  for(var i=n-1; i--;) list.push(i);

  for(var i=list.length,j;--i;){
    j = Math.random()*(i+1) | 0;
    list[i] = [list[j], list[j] = list[i]][0];
  }

  return list.slice(-m);
}

// for ES6
function generateRandomArray(num, limit=num){
  const list = [...Array(num)].map((_, i)=> i);

  for(let i=list.length,j;--i;){
    j = Math.random()*(i+1) | 0;
    [list[i], list[j]] = [list[j], list[i]];
  }

  return list.slice(-limit);
}