map 简单使用方法 作用：添加

 const arr = ['a', 'b', 'c', 'd']
            const newarr = arr.map((vluae, indax) => `<li>${indax + 1}-${vluae}</li>`)
            document.write(newarr)

filter

     let arr = [3, 13, 1, 13, 52, 351, 31, 31, 313]
            let sum = arr.filter(value => value % 2 != 0)
            console.log(sum);