javascript数组和对象的遍历、过滤

遍历数组的方法

1、常见的for循环：

var arr = [1,2,3,4];
 for(var i = 0; i < arr.length; i++){
    console.log(arr[i]);
}

2、forEach和map：

var arr = ['a', 'b', 'c', 'd'];
arr.forEach((e, i) => console.log(i, e) ); 
//0 'a'
//1 'b'
//2 'c'
//3 'd'

var arr = ['a', 'b', 'c', 'd'];
arr.map((e, i) => console.log(i, e) ); 
//0 'a'
//1 'b'
//2 'c'
//3 'd'

3、for...of

var arr = [1, 2, 3]
for(let key of arr){
    console.log(key);
}

遍历对象

1、for ... in

var xiaohua = {age: 18, height: 185, country: "China"}
for( let key in xiaohua){
   console.log(key, xiaohua[key]);
}
//age 18
//height 185
//country "China"

过滤数组

filter

var arr = [
      {key: "1", name: "小王", age: 22, address: "西湖区湖底公园1号"},
      {key: "2", name: "小张", age: 32, address: "西湖区湖底公园2号"},
      {key: "3", name: "小李", age: 42, address: "西湖区湖底公园3号"}
 ];
var ageArr = [22, 32];
// 过滤arr数组中age符合ageArr数组元素的值，即类似于删除arr表格中的第第一项和第二项
var newArr = arr.filter(item => {
    if(ageArr.indexOf(item.age) > -1){
        return;
    } else {
        return item;
    }
});
// 此时newArr为 [{key: "3", name: "小李", age: 42, address: "西湖区湖底公园3号"}]