Pick N elements from an array randomly.

randPick.js

/**
 * Pick N elements from an array randomly.
 */

function randPick(arr, n) {
  var len = arr.length;
  var randIdx;
  var tmp;
  
  while (n--) {
    randIdx = Math.floor(Math.random() * len);
    tmp = arr[len - 1];
    arr[len - 1] = arr[randIdx];
    arr[randIdx] = tmp;
    len--;
  }
  return arr.slice(len - arr.length);
}