An improved shuffle algorithm: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle

gistfile1.js

function fisherYatesShuffle(array) {
    var currentIndex = array.length
      , temporaryValue
      , randomIndex
      ;

    // While there remain elements to shuffle...
    while (0 !== currentIndex) {

      // Pick a remaining element...
      randomIndex = Math.floor(Math.random() * currentIndex);
      currentIndex -= 1;

      // And swap it with the current element.
      temporaryValue = array[currentIndex];
      array[currentIndex] = array[randomIndex];
      array[randomIndex] = temporaryValue;
    }

    return array;
  }
  
var randomChars = ['q','w','e','r','t','y','u','i','o','p','a','s','d','f','g','h','j','k','l','z','x','c','v','b','n','m'];
randomChars = fisherYatesShuffle(randomChars)
var randomString;
for (var i = 0; i< 6; i++) {
	randomString = randomString+randomChars[i];
};