5种迭代方法的作用如下：
数组还有两个归并的方法：reduce和reduceRight。这两个方法会迭代数组的所有项，最终返回一个迭代的最后值。reduce方法从数组的第一项开始迭代，reduceRight则从数组的最后一项开始。两个方法接受参数相同，都是两个参数：一个是在在每项上调用的函数以及迭代的初始值（可选）。下面，我们对reduce方法的实现进行详解。
ES6规范中Set数据结构，类似于数组，但其中的值全都是唯一的。搭配数组的迭代方法，我们能够快速方便地实现两个或多个数组的交、并、差集。
MDN web docs
ECMAScript 6入门
1、方法思路使用js数组自带的filter()方法；数据格式要求，父子节点通过，Id，ParentId进行关联。默认父结节id为0。
样例数据：var jsonData = [{"id":"1","pid":"0","name":"家用电器"}, {"id":"4","pid":"1","name":"大家电"}, {"id":"5","pid":"1","name":"生活电器"}, {"id":"2","pid":"0","name":"服饰"}, {"id":"3","pid":"0","name":"化妆"}, {"id":"7","pid":"4","name":"空调"}, {"id":"8","pid":"4","name":"冰箱"}, {"id":"9","pid":"4","name":"洗衣机"}, {"id":"10","pid":"4","name":"热水器"}, {"id":"11","pid":"3","name":"面部护理"}, {"id":"12","pid":"3","name":"口腔护理"}, {"id":"13","pid":"2","name":"男装"}, {"id":"14","pid":"2","name":"女装"}, {"id":"15","pid":"7","name":"海尔空调"}, {"id":"16","pid":"7","name":"美的空调"}, {"id":"19","pid":"5","name":"加湿器"}, {"id":"20","pid":"5","name":"电熨斗"}]
2、实现方法：
function creatTreeData(list){
var clonelist = JSON.parse(JSON.stringify(list))
var result =clonelist.filter(function(father){
var childlist = clonelist.filter(function(child){
return father.id= child.pid
})
if(childlist.length>0){
father.children=childlist
}
return father.pid ==0
})
return result
}
3、方法封装
function treeData(list,id,pid,children){
var clone = JSON.parse(JSON.stringify(list))
return clone.filter(function(father){
var childlist =clone.filter(function(child){
return father[id]==child[pid]
})
if(childlist.length>0){
father[children]=childlist
}
return father[pid]==0
})
}
