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特点:
1.类似于对象,本质上是键值对的集合
2.“键”不局限于字符串,各种类型的值(包括对象)都可以当做键
3.对象“字符串-值”,map“值-值”,是一种更加完善的hash结构实现
{
let obj = {a: 1}, obj1 = {b: 2}, obj2 = {};
obj2.c = 3;
//无论键内传什么 最终都会转换为字符串
obj2['d'] = 4;
obj2[obj] = 5;
console.log(obj.toString());//[object Object]
console.log(obj, obj1, obj2);//{a: 1} {b: 2} {c: 3, d: 4, [object Object]: 5}
}
map
{
let obj = {a: 1}, obj1 = {b: 2};
//创建一个map
const map = new Map([
['name', 'bob'],
['name', 'lucy'],//自动覆盖重复键值
['age', 18],
[obj, 'good'],
[obj1, 'bad'],
[[1, 2], 'hhh']
]);
console.log(map);//Map(5) {"name" => "lucy", "age" => 18, {…} => "good", {…} => "bad", Array(2) => "hhh"}
}
属性
{
let obj = {a: 1}, obj1 = {b: 2};
const map = new Map([
['name', 'bob'],
['name', 'lucy'],
['age', 18],
[obj, 'good'],
[obj1, 'bad'],
[[1, 2], 'hhh']
]);
console.log(map.size);//5 (重复的键值算是一个)
}
方法
1.set和get
{
let obj = {a: 1}, obj1 = {b: 2},obj2=[1,2];
const map = new Map([
[obj, 'good'],
[obj1, 'bad'],
[obj2, 'hhh']
]);
//set(支持链式编辑)
console.log(map.set('friends', ['tom', 'john']).set('num', 20));//Map(5) {{…} => "good", {…} => "bad", Array(2) => "hhh", "friends" => Array(2), "num" => 20}
console.log(map);//Map(5) {{…} => "good", {…} => "bad", Array(2) => "hhh", "friends" => Array(2), "num" => 20}
//get(不支持链式编辑)
console.log(map.get('num'));//20
console.log(map.get(obj));//good
console.log(map.get(obj2));//hhh
console.log(map.get('friends'));//(2) ["tom", "john"]
}
2.delete(不支持链式编辑)
{
let obj = {a: 1}, obj1 = {b: 2};
//创建一个map
const map = new Map([
['name', 'bob'],
['name', 'lucy'],//自动覆盖重复键值
['age', 18],
[obj, 'good'],
[obj1, 'bad'],
[[1, 2], 'hhh']
]);
console.log(map.delete('name'));//true
console.log(map.delete('xxx'));//false
console.log(map);//Map(4) {"age" => 18, {…} => "good", {…} => "bad", Array(2) => "hhh"}
}
3.has
{
const map = new Map([
['name', 'bob'],
['age', 18],
]);
console.log(map.has('name'));//true
console.log(map.has('xxx'));//false
}
4.clear
{
const map = new Map([
['name', 'bob'],
['age', 18],
]);
console.log(map.clear());//undefined
console.log(map);//Map(0) {}
}
5.keys values entries
{
const map = new Map([
['name', 'bob'],
['age', 18],
]);
console.log(map.keys());//MapIterator {"name", "age"}
console.log(map.values());//MapIterator {"bob", 18}
console.log(map.entries());//MapIterator {"name" => "bob", "age" => 18}
}
遍历
{
const map = new Map([
['name', 'bob'],
['age', 18],
]);
map.forEach(function(value,index){
console.log(index);//name; age
console.log(value);//bob; 18
})
}
注意事项
{
const map = new Map([
['name', 'bob'],
['age', 18],
]);
map.set({},'hhhh');
map.set({},'aaaa');
//会创建两个空对象
console.log(map);//Map(4) {"name" => "bob", "age" => 18, {…} => "hhhh", {…} => "aaaa"}
console.log({}==={});//false
}