.map() a Javascript ES6 Map?

Question

How would you do this? Instinctively, I want to do:

var myMap = new Map([[\"thing1\", 1], [\"thing2\", 2], [\"thing3\", 3]]);

// wishful, ignorant thinking
         


        

Answer 1

Using Array.from I wrote a Typescript function that maps the values:

function mapKeys(m: Map, fn: (this: void, v: V) => U): Map {
  function transformPair([k, v]: [T, V]): [T, U] {
    return [k, fn(v)]
  }
  return new Map(Array.from(m.entries(), transformPair));
}

const m = new Map([[1, 2], [3, 4]]);
console.log(mapKeys(m, i => i + 1));
// Map { 1 => 3, 3 => 5 }