程式碼如下：

let arr = [1, 6, 8, 3, 7, 9, 2, 7, 2, 4, 4, 3, 3, 1, 5, 3]
Array.prototype.removeDuplication = function () {
    let duplication = new Set()
    // let this = this
this.map((item, index) => {
        let lastIndexOfItem = this.lastIndexOf(item)
        while (index !== lastIndexOfItem) {
            duplication
 
.add(item)
            this.splice(lastIndexOfItem, 1)
            lastIndexOfItem = this.lastIndexOf(item)
        }
    })
    return duplication
}

console.log(arr.removeDuplication())
console.log(arr)