map.md

# Map

Map 对象保存键值对。任何值（对象或者基本类型）都可以作为一个键或一个值。

## 实例属性


### size

<!-- UTSJSON.Map.size.description -->

<!-- UTSJSON.Map.size.param -->

<!-- UTSJSON.Map.size.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('a', 'alpha');
map1.set('b', 'beta');
map1.set('g', 'gamma');
console.log(map1.size);
// expected output: 3

```

<!-- UTSJSON.Map.size.compatibility -->


## 实例方法


### clear()

<!-- UTSJSON.Map.clear.description -->

<!-- UTSJSON.Map.clear.param -->

<!-- UTSJSON.Map.clear.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('bar', 'baz');
map1.set(1, 'foo');
console.log(map1.size);
// expected output: 2
map1.clear();
console.log(map1.size);
// expected output: 0
```

<!-- UTSJSON.Map.clear.compatibility -->

### delete(key)

<!-- UTSJSON.Map.delete.description -->

<!-- UTSJSON.Map.delete.param -->

<!-- UTSJSON.Map.delete.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('bar', 'foo');
console.log(map1.delete('bar'));
// expected result: true
// (true indicates successful removal)
console.log(map1.has('bar'));
// expected result: false
```

<!-- UTSJSON.Map.delete.compatibility -->

### forEach(callbackfn, thisArg?)

<!-- UTSJSON.Map.forEach.description -->

<!-- UTSJSON.Map.forEach.param -->

<!-- UTSJSON.Map.forEach.returnValue -->

<!-- UTSJSON.Map.forEach.compatibility -->

```ts

let mapObj = new Map<string,any>()
mapObj.put("name","zhangsan")
mapObj.put("age",12)
// 需要特别注意迭代方法的第一个参数是value.第二个是key. 
mapObj.forEach(function(value:any,key:string){
    console.log(key)
    console.log(value)
})
```

### get(key)

<!-- UTSJSON.Map.get.description -->

<!-- UTSJSON.Map.get.param -->

<!-- UTSJSON.Map.get.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('bar', 'foo');

console.log(map1.get('bar'));
// expected output: "foo"
```

<!-- UTSJSON.Map.get.compatibility -->

### has(key)

<!-- UTSJSON.Map.has.description -->

<!-- UTSJSON.Map.has.param -->

<!-- UTSJSON.Map.has.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('bar', 'foo');

console.log(map1.has('bar'));
// expected output: true

console.log(map1.has('baz'));
// expected output: false
```

<!-- UTSJSON.Map.has.compatibility -->

### set(key, value)

<!-- UTSJSON.Map.set.description -->

<!-- UTSJSON.Map.set.param -->

<!-- UTSJSON.Map.set.returnValue -->

```ts
const map1 = new Map<string,string>();
map1.set('bar', 'foo');

console.log(map1.get('bar'));
// expected output: "foo"

console.log(map1.get('baz'));
// expected output: null
```

<!-- UTSJSON.Map.set.compatibility -->

注意：由于Map的key是唯一的，给同一个key多次set值时，会用新值替换老值。
```ts
const map1: Map<string,string> = new Map(); //定义一个map，key为string类型，value也是string类型
map1.set('key1', "abc");
map1.set('key1', "def");
console.log(map1.get('key1')) //返回 def
```

## 常见操作

- 创建map
```ts
let map = new Map<string,any>()
map.set("name","zhangsan")
map.set("age",12)
//Map(2) {"name":"zhangsan","age":12}
console.log(map)
```
- 通过key访问map元素
```ts
let map = new Map<string,any>()
map.set("name","zhangsan")
map.set("age",12)
let nameVal = map['name']
//zhangsan
console.log(nameVal)
```
- 遍历map
```ts

let map = new Map<string,any | null>()
map.set("name","zhangsan")
map.set("age",12)

// 遍历函数 1
map.forEach(function(value:any | null){
    console.log(value)
})
// 遍历函数 2
map.forEach(function(value:any | null,key:string){
    console.log(key)
    console.log(value)
})
// 遍历函数 3
map.forEach(function(value:any | null,key:string,map: Map<string,any | null>){
    console.log(value)
    console.log(key)
    console.log(map)
})

```

<!-- UTSJSON.Map.tutorial -->