JS: Map Constructor

New in JS2015.

new Map()

Create a empty map.

const xmap = new Map();

// add new item
xmap.set(1, "n1");
xmap.set(2, "n2");

console.log(xmap);
// Map(2) { 1 => "n1", 2 => "n2" }

new Map(iterable)

Create a map from values in Iterable Object.

// use nested array as literal expression for map
const xmap = new Map([[3, "n3"], [4, "n4"]]);
console.log(xmap);
// Map(2) { 3 => "n3", 4 => "n4" }