The size accessor property of Map instances returns the number of elements in this map.
Description
The value of size is an integer representing how many entries the Map object
has. A set accessor function for size is undefined; you can not change this
property.
Examples
Using size
const myMap = new Map();
myMap.set("a", "alpha");
myMap.set("b", "beta");
myMap.set("g", "gamma");
console.log(myMap.size); // 3