What is the map.keys() method in TypeScript?

// Create some maps 
let evenNumbers = new Map<string, number>([["two", 2], ["four", 4], ["eight", 8]])
let cart = new Map<string, number>([["rice", 500], ["bag", 10]])
let countries = new Map<string, string>([["NG", "Nigeria"], ["BR", "Brazil"], ["IN", "India"]])
let isMarried = new Map<string, boolean>([["James", false], ["Jane", true], ["Doe", false]])
let emptyMap = new Map<null, null>()
// get the iterators
let itr1 = evenNumbers.keys()
let itr2 = cart.keys()
let itr3 = countries.keys()
let itr4 = isMarried.keys()
let itr5 = emptyMap.keys()
// log out the iterators
console.log(itr1)
console.log(itr2)
console.log(itr3)
console.log(itr4)
console.log(itr5)
// log out values for any of the iterators
for (let value of itr1) {
    console.log(value); 
}