初探ES6中的Map和WeakMap

let myMap=new Map();
let keyObj={},keyfunc=function(){},keysTring='hello word';

myMap.set(keysTring,'keysTring的关联值')
myMap.set(keyfunc,'keyfunc的关联值')
myMap.set(keyObj,'keyObj的关联值')

console.log(myMap.size)  //3

console.log(myMap.get(keysTring)) //keysTring的关联值
console.log(myMap.get('hello word')) //keysTring的关联值


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console.log(myMap.get(keyfunc)) //keyfunc的关联值
console.log(function(){}===keyfunc)  //false 
console.log(myMap.get(function(){})) //undefined, 因为keyFunc !== function () {}


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console.log(myMap.get(keyObj)) //keyObj的关联值
console.log({}===keyObj)  //false 
console.log(myMap.get({})) //undefined 因为keyObj !== {}

myMap.set(NaN, "not a number");
console.log(myMap.get(NaN))  //not a number

var otherNaN=Number('foo');
console.log(otherNaN)  //NaN
console.log(myMap.get(otherNaN))  //not a number 也可以取值

let kvArray = [["key1", "value1"], ["key2", "value2"]];
var myMap1 = new Map(kvArray);
//使用映射对象常规的构造函数将一个二维键值对数组对象转换成一个映射关系
console.log(myMap1) //Map { 'key1' => 'value1', 'key2' => 'value2' }
console.log(myMap1.get('key1'))  //value1
console.log([...myMap1]) //[ [ 'key1', 'value1' ], [ 'key2', 'value2' ] ]

var myMap2 = new Map(kvArray);
myMap2.forEach((value,index)=>{
    console.log(value+'---'+index)  //value1---key1   value2---key2
})

var myMap3 = new Map(kvArray);
for(var a of myMap3){
    console.log(a)      //[ 'key1', 'value1' ] [ 'key2', 'value2' ]
}

for(var [key,value] of myMap3){
    console.log('key:'+key+', value:'+value)  //key:key1, value:value1 key:key2, value:value2
}

let clearMap=new Map();
clearMap.set('hello','word');
console.log(clearMap.size)  //1
clearMap.clear();   //清空
console.log(clearMap.size)  //0

let delMap=new Map();
delMap.set('hi','word');
delMap.set('hello','word');
console.log(delMap)  //Map { 'hi' => 'word', 'hello' => 'word' }
delMap.delete('hi'); //执行删除操作
console.log(delMap)  //Map { 'hello' => 'word' }

let hasMap=new Map();
hasMap.set('hi','word');
hasMap.set('hi','hello word');
console.log(hasMap)  //Map { 'hi' => 'hello word' }   一样的key后面的value会覆盖前面的值
console.log(hasMap.has('hi')); //true
console.log(hasMap.has('hello')); //false

let entriesMap=new Map();
entriesMap.set('a','A');
entriesMap.set('b','B');
let entries=entriesMap.entries();
console.log(entries.next()); //{ value: [ 'a', 'A' ], done: false }
console.log(entries.next().value); //[ 'b', 'B' ]
console.log(entries.next()); //{ value: undefined, done: true }

let valueMap=new Map();
valueMap.set('a','A');
valueMap.set('b','B');
let values=valueMap.values();
console.log(values.next())  //{ value: 'A', done: false }
console.log(values.next())  //{ value: 'B', done: false }
console.log(values.next())  //{ value: undefined, done: true }

1.delete(key); 根据key删除value
2.get(key);根据key获取value
3.has(key) 根据key检查是不是存在value
4.set(key,value) 根据key设置value

let weakMap=new WeakMap();
weakMap.set('hi','word')  //异常   因为WeakMap的键只能是个对象
let obj1={};
weakMap.set(obj1,'word')  //正常
console.log(weakMap)   //WeakMap {}
console.log(weakMap.get(obj1))  //word
console.log(weakMap.has(obj1))  //true
console.log(weakMap.delete(obj1))  //true