map + filter 快速操作對象數組去重

var tableData = [
	{date:'20200224', value:100},
	{date:'20200224', value:200},
	{date:'20200225', value:100},
	{date:'20200225', value:300},
	{date:'20200225', value:400},
	{date:'20200226', value:200},
]


function filtersDate(data){
	return data.map(item => item.date).filter((el, index, arr) => {
       return arr.indexOf(el) === index
    })
}

console.log(filtersDate(tableData))

/* 輸出 */
['20200224', '20200225', '20200226']