js数组去重

1、定义一个新数组，并存放原数组的第一个元素，然后将元素组一一和新数组的元素对比，若不同则存放在新数组中。

    var arr = [1,2,3,1,2,5,4,5,2,1,2,3,1,2,1]; 
    var arrr = [1]; 
    for(var i=0;i<arr.length;i++){
        var flag = false; 
        for(var j=0;j<arrr.length;j++){ 
            if (arr[i] == arrr[j]) { 
                flag = true; 
                break; 
            } 
        }
        if (!flag) { 
            arrr.push(arr[i]); 
        } 
    }
    console.log(arrr)

2、先将原数组排序，在与相邻的进行比较，如果不同则存入新数组

    // 将原数组排序组成新的数组 
    var arr = [1,2,3,1,2,5,4,5,2,1,2,3,1,2,1]; 
    var arr2 = arr.sort();
    var res = [arr2[0]]; 
    for(var i=0;i<arr2.length;i++){ 
        if (arr2[i] !== res[res.length-1]) { 
            res.push(arr2[i]); 
        } 
    }
    console.log(res);

3、利用对象的属性去重（推荐）

    var arr = [1,2,3,1,2,5,4,5,2,1,2,3,1,2,1]; 
    var res = []; 
    var json = {}; 
    for(var i=0;i<arr.length;i++){ 
        if (!json[arr[i]]) { 
            res.push(arr[i]); 
            json[arr[i]] = 1; 
        }
    }
    console.log(res);

4、利用下标查询

    var arr = [1,2,3,1,2,5,4,5,2,1,2,3,1,2,1]; 
    var newArr = [arr[0]]; 
    for(var i=1;i<arr.length;i++){ 
        if (newArr.indexOf(arr[i]) == -1) { 
            newArr.push(arr[i]); 
        } 
    }
    console.log(newArr)

5、利用ES6方法 - set去重

    var arr = [1,2,3,1,2,5,4,5,2,1,2,3,1,2,1];  
    function fn(arr){
        var s = new Set(arr); 
        return Array.from(s); 
    }
    console.log(fn(arr))

 6、数组对象去重

function unique(arr) {
     const res = new Map();
     return arr.filter((arr) => !res.has(arr.orderNumber) && res.set(arr.orderNumber, 1))
}
let arr = [
    {"tid": "1476441758236913665", "state": 1, "orderNumber": "HK-2020050065"},
    {"tid": "1476442625975496706", "state": 1, "orderNumber": "HK-2020060223"},
    {"tid": "1476442749619384321", "state": 1, "orderNumber": "HK-2020060223"},
    {"tid": "1476443010194714625", "state": 1, "orderNumber": "HK-2020060221"},
    {"tid": "1476444086746722306", "state": 1, "orderNumber": "HK-2020060221"},
    {"tid": "1476444379194568706", "state": 1, "orderNumber": "HK-2020060221"}
]
let newArr = unique(arr) //调用方法
console.log(newArr)