js的数组map方法,遍历map集合的方法

map 方法：可以简单的理解为映射

var num = [1,2,3,4];var dataAdd = num.map(n => n+n);var datadeep = num.map(n => n-1);console.log(dataAdd);//[2, 4, 6, 8]console.log(datadeep);//[0,1,2,3]

filter方法: 过滤筛选的作用，数组filter后，返回的结果为新的数组

var chinaWords = [{name:"君住长江头",msg:"诗词",age:15},{name:"我住长江尾",msg:"歌赋",age:15},{name:"日日思君不见君,同饮一江水",msg:"古风",age:14}]var dataname = chinaWords.map(one => one.name)console.log(dataname.join(','));//君住长江头,我住长江尾,日日思君不见君,同饮一江水var oneages = chinaWords.map(one => one.age)console.log(oneages.join(','));//15,15,14var ageJudge = oneages.filter(age => age > 14 )console.log(ageJudge.join(','));//15,15

filter() 去掉空字符串、undefined、null

let arr = ['','1','2',undefined,'3.jpg',undefined]let newArr = arr.filter(item => item)console.log(newArr)

filter()数组去重

let array = [1,3,5,5,7,7,7,8,9];function unique(arr) { return arr.filter(function(item, index, arr) { return arr.indexOf(item, 0) === index; });}unique(array);//[1,3,5,7,8,9];