数组去重

const arr=[1,3,4,56,6,7,8,8,,56,5,4,4,3,2,1]
for (var i = arr.length - 1; i > 0; i--) {
        for (var j = 0; j < i - 1; j++) {
            if (arr[i] == arr[j]) {
                arr.splice(i, 1)
            }
        }
    }
    console.log(arr);