set和map

set数据结构【一个属性：size；常用的四个方法：

add()，delete()，clear()，has()

】

size：set属性，set的数据大小

let set1 = new Set();
console.log(set1.size);//结果：0

add():添加数据【返回集合对象，支持链式操作】

let r1 = set2.add("lea");
console.log(set2);//结果：Set(4) {1, 2, "3", "lea"}
console.log(r1);//结果：Set(4) {1, 2, "3", "lea"}

delete()：删除某项【不能链式操作】

let r2 = set2.delete(1);
console.log(r2);//结果：true【删除成功】
console.log(set2);//结果：Set(3) {2, "3", "lea"}
console.log(set2.delete(1));//结果：false【删除失败】

clear()：清除集合数据

let r3 = set2.clear();
console.log(set2);//结果：Set(0) {}
console.log(r3);//结果：undefined

has():是否存在某个值

let r4 = set2.has(1);
console.log(r4);//结果：false

map：键值对，键不只可以是字符串,也可以是其他类型的键

①、普通对象示例：

js:

//object对象的键只能是字符串，
let obj0={a:1},obj1={b:1};
obj0.name = "lea";
obj0[obj1] = "test";
obj0[obj0] = "test2";//替代上一项【证明object的键只会是字符串，对象会把键直接转为字符串】
console.log(obj0);

②、新建map:new Map( {   [key:value],   [key:value],   [key:value], ........   }   );

js:【注意点：key为"name",只会保留一个】

let map0 = new Map([
    ["name","lea"],
    ["tel","13452312321"],
    ["age","23"],
    ["name","anna"],
    [obj0,"lea"],
    [obj1,"lea"]
]);
//key可以是对象；
console.log(map0);

示例①，②结果：

map实例的属性和方法

属性：size：获取数据的长度
方法：【
set():增加或修改数据【语法：set(key,value);】，

get(key):查看某项数据。

delete(key):删除数据

】
js:

let obj0={a:1},obj1={b:1};
let map0 = new Map([
    ["name","lea"],
    ["tel","13452312321"],
    ["age","23"],
    ["name","anna"],
    [obj0,"lea"],
    [obj1,"lea"]
]);
//增加:
map0.set("add",["湖北省","荆州市"]);
map0.set(["province","city"],"湖北省荆州市");
//修改
map0.set("name","joanna");
console.log(map0);
//get(key):查看某项数据。
console.log(map0.get("name"));
//delete():删除数据
console.log(map0.delete("name"));
console.log(map0);

结果：

方法：【

has(key):是否存在该键值对

clear():清空

】

js:

let obj0={a:1},obj1={b:1};
let map0 = new Map([
    ["name","lea"],
    ["tel","13452312321"],
    ["age","23"],
    ["name","anna"],
    [obj0,"lea"],
    [obj1,"lea"]
]);
//has(key):是否存在该键值对
console.log(map0.has("name"));//true
console.log(map0.has(obj0));//true
console.log(map0.has("add"));//false
//clear():清空
map0.clear();
console.log(map0.size);//0

result:

方法：【

//keys(),values(),entries()

】

js:

let obj0={a:1},obj1={b:1};
let map0 = new Map([
    ["name","lea"],
    ["tel","13452312321"],
    ["age","23"],
    ["name","anna"],
    [obj0,"lea"],
    [obj1,"lea"]
]);
console.log(map0.keys());
console.log(map0.values());
console.log(map0.entries());

result: