js数组操作

附：数组操作api

https://www.runoob.com/jsref/jsref-obj-array.html

js数组中的find、filter、forEach、map四个方法的详解和应用实例

https://blog.youkuaiyun.com/lhjuejiang/article/details/80112547

1.判断数组里是否有某个字段，有就删除，没有就添加

      var ccc = [1,2,3,4,5,6,7,8,9]
      var ndx = ccc.findIndex(function(ele) { return ele == 10 });
      if (ndx > -1) {
          ccc.splice(ndx, 1);
        } else {
          ccc.push(10);
        }
        //[1,2,3,4,5,6,7,8,9,10]

2.树形数组判断某个字段并更改

var arr = [{
	"type": 1,
	"children": [{
		"type": 1,
	}]
}, {
	"type": 1,
	"children": [{
		"type": 1,
		"children": [{
			"type": 1,
		}, {
			"type": 2,
		}, {
			"type": 1,
			"children": [{
				"type": 2,
			}]
		}]
	}]
}]
//判断type，为1显示分类，，为2显示卡片
function formatter(arr) {
      return arr.map(function(v) {
        return {
        ...v,
            type: v.type == 1 ? "分类" : "卡片",
            children: v.children ? formatter(v.children) : undefined
        }
      })
    },
console.log(formatter(arr))

3.只取数组的前几个，后面的不要(slice() 方法)

ps:填入数字如果是负数就是从后面算起（如：（-1，-3）就是倒数第一个开始到倒数第三个）

var aaa = [1,2,3,4,5,6,7,8,9,10]
var bbb = aaa.slice(0,5)
bbb//[1, 2, 3, 4, 5]



var aaa = [1,2,3,4,5,6,7,8,9,10]
var ccc = [1,2,3]
var bbb = ccc.slice(0,5)
bbb//[1, 2, 3]