数组去重

let arr = [12,43,23,43,68,12];
let item = [...new Set(arr)];
console.log(item);//[12, 43, 23, 68]

let arr = [12,43,23,43,68,12];
let item = new Set(arr);
console.log(item);//结果输出的是一个对象

//使用Array.from转成数组

let arr = [12,43,23,43,68,12];
let item = Array.from(new Set(arr));
console.log(item);// [12, 43, 23, 68]

function unique3(arr){
    for (var i =0,hash=[];i<arr.length ;i++ ){
        if (hash[arr[i]]==undefined){
        hash[arr[i]]=1;
        } 
    }
    var j=0;
    var keys=[];
    for (keys[i++] in hash );
    return keys;
}
console.log( unique3(arr) );