数组去重

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique1(arr){
  return Array.from(new Set(arr));
}

console.log(unique1(arr));

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique2(arr){
  var len = arr.length;
    var res = [];
    for(var i = 0; i< len; i++ ){
     for(var j = i+1; j < len ;j++){
           if(arr[i] == arr[j]){
                j = ++i;
         }
        }
        res.push(arr[i]);
    }
    return res;
}

console.log(unique2(arr));

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique3(arr){
   var len = arr.length;
    var obj = {};
    var res = [];
    for(var i = 0; i < len; i++){
     if(!obj[arr[i]]){
            obj[arr[i]] = 1;
         res.push(arr[i]);
        }
    }
    return res;
}

console.log(unique3(arr));

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique4(arr){
  var len = arr.length;
    for(var i = 0; i < len; i++){
     for(var j = i + 1; j < len ; j ++){
           if(arr[i] == arr[j]){
                arr.splice(j,1);
             len -- ;
             j--;
         }
        }
    }
    return arr;
}

console.log(unique4(arr));//占用内存高不推荐

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique5(arr){
    var len = arr.length;
    var res = [];
    arr.forEach(function(v, i ,arr){
      var bool = arr.indexOf(v,i+1);  //从传入参数的下一个索引值开始寻找是否存在重复
          if(bool === -1){
          res.push(v);
        }
  })
   return res;
}

console.log(unique5(arr));

var arr = [1,3,54,67,87,34,54,33,23,54,23,2,2,1,5];

function unique6(arr){
   var len = arr.length;
    arr.sort(function(a,b){  //对数组进行排序才能方便比较
   return a - b;
  })
   function loop(index){
        if(index >= 1){
           if(arr[index] === arr[index-1]){
             arr.splice(index,1);
         }
            loop(index - 1); //递归loop函数进行去重
      }
    }
    loop(len-1);
 return arr;
}

console.log(unique6(arr));