遍历数组中的数据的方法

var books = [{name:'西游记',author:'吴承恩',price: 58,count:5},{name:'三国演义',author:'罗贯中',price: 68,count: 6},{name:'水浒传',author:'施耐庵',price: 48,count:8},{name:'红楼梦',author:'曹雪芹',price: 78,count:10}]
(1) 通过for循环 计算总价格

let totalPrice = 0
for(let i=0;i<this.books.length;i++) {
    this.totalPrice += this.books[i].price * this.books[i].count
}

(2)

let totalPrice = 0
for(let i in this.books) {
    this.totalPrice += this.books[i].price * this.books[i].count
}

(3)

let totalPrice = 0
for(let item of this.books) {  // item为每一项的下标
    totalPrice += item.price * item.count
}

(4) forEach

let totalPrice = 0
this.books.forEach(item => {
    totalPrice += item.price * item.count
})

(5) map 返回一个新数组

let totalPrice = 0
this.books.map(item => {
    return totalPrice += item.price * item.count
})

(6) reduce函数的作用：对数组中所有的内容进行汇总