Reverse an ES6 Map

Question

Suppose I have created a Map object like this Map {"a" => "apple", "b" => "banana"}:

m = new Map([ ["a", "apple"], ["b", "banana"] ]);

Now I want to reverse it and get Map {"b" => "banana", "a" => "apple"}

I see the only way to do it as follows:

new Map(Array.from(m.entries()).reverse());

which doesn't look neither concise nor straightforward. Is there a nicer way?

Solution 1

How about new Map([...m].reverse());?

let m = new Map([['a', 'apple'], ['b', 'banana']]);
let r = new Map([...m].reverse());

console.log([...m]);
console.log([...r]);

Solution 2

You can drop the .entries() call as that's the default iterator of maps anyway:

new Map(Array.from(m).reverse())

Which actually seems both concise and straightforward to me - convert the map to a sequence, reverse that, convert back to a map.