Mapping a Map: spread vs manual performance

foo.js

(() => {
const IterableH = {
    map: fn => iterable => [...iterable].map(fn),
};

const MapH = {
	map: fn => map => new Map(IterableH.map(([ key, value ]) => [ key, fn(value) ])(map)),
	map2: fn => map => {
        const newMap = new Map()
        for ([ key, value ] of map) {
            newMap.set(key, fn(value))
        }
        return newMap;
    },
}

const map = new Map(_.range(0, 1000).map(x => [ x, x ]))

console.time('map');
MapH.map(value => value + 1)(map);
console.timeEnd('map');

console.time('map2');
MapH.map2(value => value + 1)(map);
console.timeEnd('map2');
})()

Testing in Chrome 57 beta:

map: 1.68ms
map2: 0.983ms