Map: initialize

initialize a Map

a new Map() is empty, has size=0

const mapSize = new Map(); assert.equal(mapSize, 0);

init Map with [[]] has a size=1

const mapSize = new Map().size; assert.equal(mapSize, 1);

init a Map with [[1]] is the same as map.set(1, void 0)

let map1 = new Map(); let map2 = new Map().set(1, void 0); assert.deepEqual(map1, map2);

init Map with multiple key+value pairs

const pair1 = [1, 'one']; const pair2 = [2, 'two']; const map = new Map(); assert.deepEqual(map, new Map().set(...pair1).set(...pair2));

keys are unique, the last one is used

const pair1 = [1, 'one']; const pair2 = [1, 'uno']; const pair3 = [1, 'eins']; const pair4 = [2, 'two']; const map = new Map([pair3, pair1, pair2, pair4]); assert.deepEqual(map, new Map().set(...pair3).set(...pair4));

init Map from an Object, is a bit of work

let map = new Map(); const obj = {x: 1, y: 2}; const keys = Object.keys(obj); keys.forEach(key => map.set()); assert.deepEqual(map, new Map([['x', 1], ['y', 2]]));

Required Knowledge

• `let` declaration (Block scope)
• `const` declaration (Block scope)
• `Array.from()` (Array API)
• basics (Map)
• `map.set()` (Map)

Related Katas

Map

• basics
• map.get()
• map.set()
• initialize
• map.has()

Difficulty Level

ADVANCED

First Published

22 June 2015

Stats

6 tests to solve