将数组中重复次数大于1的元素列出来（Map思路）

function duplicates(arr) {
    let map = new Map();
    let resultMap = arr.reduce((prev, curr) => {
        return prev.set(curr, prev.get(curr) + 1 || 1);
    }, map);
    let list = [];
    for (let [key, value] of resultMap) {
        if (value > 1) {
            list.push(key);
        }
    }
    console.log(resultMap)
    return list;
}

console.log(duplicates([1, 2, 4, 4, 3, 3, 1, 5, 3]))