在项目中经常要用到 js 循环数组的操作，要多练习：

let arr = [{name: 'Maly'},'bbb',undefined, ,''];
// arr.prototype.abc = '111';

//for 循环，顺序遍历
for(let i=0; i<arr.length; i++){
console.log('for:',arr[i]);
}

//forEach() E大写
arr.forEach(function(item){
console.log('forEach: ',item);
})

// for ...in
for(let index in arr){
console.log('for ...in : ',index)
// console.log('for ...in : ',arr[index])
}
console.log("\n");
//for ...of
for(let item of arr){
console.log('for of : ',item);
}

练习的在线js编辑器工具：https://www.jsrun.net/new
参考文章：js 循环有哪些？

灵活组织数据

let book = [
{id:192, name:'鲁滨逊漂流记'},
{id:195, name:'格列夫游记'},
];
const lendCart = [
{id:1,member_id:35,book_id:192,num:1},
{id:2,member_id:35,book_id:195,num:3},
];

let myBookList = [];
lendCart.forEach((item)=>{
myBookList.push({
bookId:item.book_id,
carId: item.id
})
}

);

console.log(myBookList);