ImmutableJS: Convert List to indexed Map

Question

This question is about Immutable.js library.

I have a List<T>, where T is {name: string, id: number}. I want to convert it to Map<number, T>, with id of T to the keys. Using standard method toMap gives me a Map with sequential indexes, and there is no way to hook there. And no method like indexBy or other. how to do that?

Answer 1

You can do it with a reducer like this:

function indexBy(iterable, searchKey) {
    return iterable.reduce(
        (lookup, item) => lookup.set(item.get(searchKey), item),
        Immutable.Map()
    );
}

var things = Immutable.fromJS([
    {id: 'id-1', lol: 'abc'},
    {id: 'id-2', lol: 'def'},
    {id: 'id-3', lol: 'jkl'}
]);
var thingsLookup = indexBy(things, 'id');
thingsLookup.toJS() === {
  "id-1": { "id": "id-1", "lol": "abc" },
  "id-2": { "id": "id-2", "lol": "def" },
  "id-3": { "id": "id-3", "lol": "jkl" }
};