获取数组重复元素方法

使用indexOf实现去重和获取重复元素

const arr = [1, 2, 2, 3, 4, 3, 2, 4];
function fn1 (arr) {
    let ary = [];
    let ary2 = [];
    for (let i = 0; i < arr.length; i++) {
        const cur = arr[i];
        if (ary.indexOf(cur) === -1) {
            ary.push(cur)
        } else {
            ary2.push(cur)
        }
    }
    return ary2;
}
fn1(arr);
// [2, 3, 2, 4]

比较2个相近元素实现去重和获取重复元素

const arr = [1,2,3,2,3,4,4,2,4];
function fn(arr){
    arr = arr.sort()
    let res = [];
    let unRes=[];
    for (let i = 0; i < arr.length; i++) {
        if (arr[i] === arr[i - 1]) { // arr[i] !== arr[i - 1] 去重
            res.push(arr[i])
        }
    }
   return unRes
}

fn(arr);
// [2, 2, 3, 4, 4]