Sort JavaScript map by decimal key

Question

I have a map with keys as months and key values ​​as 1...31. If I understand correctly, JavaScript converts the map's keys to strings. After sorting using standard newMap([...myMap.entries()].sort()), the map is sorted by key as follows: 1,11,12,13,...,19,2,20,21,22 ,23,...29,3,30,31. I found a way to convert the decimal keys to strings and pad the single numbers with 0's to achieve 1,2,3,4,5,.

P粉501683874 · Answer

Although any type can be used in the key of a Map() object, they are coerced when using the default sort() implementation Convert to string.

To solve this problem, you need to implement your own sorting logic to explicitly compare them as numerical values. In the example below it uses integers, but this can be easily updated to use parseFloat() if decimal comparisons are required.

const map = new Map();
map.set(3, "foo");
map.set(1, "foo");
map.set(8, "foo");
map.set(10, "foo");
map.set(5, "foo");
map.set(2, "foo");
map.set(4, "foo");
map.set(7, "foo");
map.set(6, "foo");
map.set(9, "foo");

// does not work:
const mapFailedSort =  new Map([...map.entries()].sort());
console.log(mapFailedSort);

// works:
const mapAsc = new Map([...map.entries()].sort((a, b) => +a[0] > +b[0] ? 1 : -1));
console.log(mapAsc)

Note: The code snippet console appears to be incompatible with Map() objects - please check the output in the dev tools console to see if the ordering is correct.