Javascript 洗牌算法,打乱数组,随机获取元素

//利用洗牌算法
Array.prototype.shuffle=function(){
  var i,t,m=this.length;
  while(m){
    i=Math.floor(Math.random()*m--);
    t=this[m];
    this[m]=this[i];
    this[i]=t;
  }
  return this;
}

var arr=[1,2,3,4,5];
console.log(arr.shuffle());
console.log(arr.slice(0,2));