三种方法实现数组去重

Array.prototype.unique1 = function(){
    var arr = [];
    for(var i = 0;i<this.length;i++){
      if(!arr.includes(this[i])) arr.push(this[i])
    }
    return arr;
  }

  Array.prototype.unique2 = function(){
    var hash = {},
        arr = [];
    for(var i=0;i<this.length;i++){
      if(!hash[this[i]]){
        hash[this[i]] = true;
        arr.push(this[i])
      }
    }
    return arr;
  }

  Array.prototype.unique3 = function(){
    var arr = [];
    arr[0] = this[0];
    for(var i=1;i<this.length;i++){
      if(this.indexOf(this[i]) == i) arr.push(this[i])
    }
  return arr;
  }