javascript map forEach filter some every在购物车中的实战演练区分用法

1.map forEach

1.map 循环遍历每一项，返回一个新的数组

例: 购物车商品小计：

//购物车
var cart=[
  {"id":101,"name":"大米","count":1,"price":3.3,"check":1},
  {"id":102,"name":"小米","count":2,"price":3.3,"check":1},
  {"id":103,"name":"二米","count":3,"price":3.3,"check":1},
]
//每个购物车中的小计
var cartPrices =cart.map(item=>{
  return (item.count*item.price).toFixed(2)
})
console.log(cartPrices); 

2.forEach 循环遍历每一项，并不返回值

例：计算商品价格的总和：

//购物车
var cart=[
  {"id":101,"name":"大米","count":1,"price":3.3,"check":1},
  {"id":102,"name":"小米","count":2,"price":3.3,"check":1},
  {"id":103,"name":"二米","count":3,"price":3.3,"check":1},
]
//每个购物车中的小计
var cartPrices = cart.map(item=>{
  return (item.count*item.price).toFixed(2)
})
//计算总和
var totalPrice = 0
cartPrices.forEach((item,index)=>{
  totalPrice+=parseFloat(item);
})
console.log(totalPrice.toFixed(2));
 

2.filter 过滤出正确的那一项

例: 显示购物车信息

 //商品ID
var id = 101;//101胶水'.'
//购物车
var cart=[
  {"id":101,"name":"大米","count":1,"price":3.3,"check":1},
  {"id":102,"name":"小米","count":2,"price":3.3,"check":1},
  {"id":103,"name":"二米","count":3,"price":3.3,"check":1},
]
//过滤出该商品信息
var goods = cart.filter(item=>{
  return item.id == id;
})
console.log(goods);

3.some 和 every 过滤每一项是否有正确的

1.some 如果有满足条件返回true不在向下执行 ，如果没有满足条件返回false

例: 购物车是否选中

  //商品ID
var id = 101;//101胶水'.'
//购物车
var cart=[
  {"id":101,"name":"大米","count":1,"price":3.3,"check":0},
  {"id":102,"name":"小米","count":2,"price":3.3,"check":1},
  {"id":103,"name":"二米","count":3,"price":3.3,"check":1},
]
//过滤购物车商品是否选中状态
var ischeck = cart.some(item=>{
  if(item.id == id){
    return item.check;
  }
})
console.log(ischeck)

2.every 数组的每一项是否都满足条件返回true,否则返回false

例:购物车商品是否全选状态

//商品ID
var id = 101;//101胶水'.'
//购物车
var cart=[
  {"id":101,"name":"大米","count":1,"price":3.3,"check":1},
  {"id":102,"name":"小米","count":2,"price":3.3,"check":0},
  {"id":103,"name":"二米","count":3,"price":3.3,"check":1},
]
//过滤购物车商品是否选中状态
var isallcheck = cart.every(item=>{
    return item.check;
})
console.log(isallcheck)