ES6 map extract array object

See code snippet

var list= [{
    name:' Zhang San ',age:16},{
    name:' Zhao si ',age:18}];
var nameList = list.map(a=>a.name)//[' Zhang San ',' Zhao si ']
var ageList = list.map(a=>a.age)//[16,18]

Often used in scenes Pick up the price of all goods in the shopping cart 、 Extract the product pictures in the product list and so on

var list= [{
    name:' Zhang San ',age:16},{
    name:' Zhao si ',age:18}];
var nameList = [];
var ageList = [];
list.forEach(item=>{
    
	if(item.name)
	nameList.push(item.name)
	if(item.age)
	ageList.push(item.age)
})
nameList //[' Zhang San ',' Zhao si ']
ageList //[16,18]

use map Than forEach It can be more efficient and save time , Save code

By the way map and forEach What they have in common and what they don't have in common

 The same thing 
(1) They loop through every item in the array .
(2) Each execution of an anonymous function supports three parameters , The parameters are item( At present, every item ),index( Index value ),arr( Original array ).
(3) In anonymous functions this Is directed window.
(4) Only arrays can be traversed .
(5)forEach  and  map It's equivalent to a single-layer package for loop 
 Difference 
(1)map() Allocates memory space to store the new array and returns ,forEach() No data will be returned .
(2)forEach() allow callback Change the elements of the original array .map() Return a new array .