JSFiddle - React, Tailwind, and code Playground

JavaScript

const m1 = new Map([
  ["a", "a1"],
  ["b", "b1"],
  ["c", "c1"]
]);
const m2 = new Map([
	["b", "b2"],
  ["c", "c2"]
]);
const m3 = new Map([
	["c", "c3"]
]);
const m4 = new Map([...m1, ...m2, ...m3]);
console.log(m4);