1.size attribute: Returns the total number of structural members Map
const map = new Map([
[ 'Name', 'John Doe'],
['title','Author']
])
console.log(map.size) // 2
2.set and get
3.has method: returns a Boolean value, a key to determine whether the object them in the current Map
map.has('name') //true
4.delete method - returns true success
5. The method of traversing --- 3 walker generating function, a traversal methods
keys () - Returns the key names walker
values () - Returns the key iterator
entries () - Returns all members of the walker
forEach () - all members of traversing Map
