.size

The .size property returns the number of entries inside of a Map object.

map.size;

Since .size is a property of Map, no parentheses are needed.

Assuming there is a map of fruits, the number of keys can be checked with the .size property:

const fruits = new Map([
  ['Apples', 5],
  ['Oranges', 8],
]);

console.log(fruits.size); // Output: 2