JS Map

Create map

//MAPS = key-val pairs - can use ANY type as a key or value
const map1 = new Map();

将key，value传入map

//Set Keys
const key1=`some string`,
      key2={},
      key3=function(){};
//Set map values by key
map1.set(key1,'Value of key1');
map1.set(key2,'Value of key2');
map1.set(key3,'Value of key3');

通过key得到map中的val

//Get value by key
console.log(map1.get(key1));
console.log(map1.get(key2));
console.log(map1.get(key3));

map.size

//Count values
console.log(map1.size); //size 

遍历map(for of)

for (let [key,value] of map)

//Loop using for...of to get keys and values
for(let [key,value] of map1){
  console.log(`${key} = ${value}`);
}

for (let key of map.keys())

// Iterate keys only
for(let key of map1.keys()){
  console.log(key);
}

for (let value of map.values())

//Iterate values only
for(let value of map1.values()){
  console.log(value);
}

注意点
for in 返回键名；
for of 返回元素；

foreach 遍历map

参数val在前，key在后；

//Loop with forEach
map1.forEach(function(val,key){
  console.log(key,val);
})

Map 转为 array

Array.from(map)

//Convert to Arrays

//Create an array of the key value pairs
const keyValArr=Array.from(map1);
console.log(keyValArr); //得到嵌套array