Doing some neat typescript stuff.

filterMap.ts

type FilterFn<T> = (item: T) => boolean;
type FilterMap<T> = Record<string, FilterFn<T>>;

function filterMap<T, U extends FilterMap<T>>(items: T[], filterMap: U) {
    const filters = new Map<string, FilterFn<T>>();
    Object.keys(filterMap).forEach((key) => filters.set(key, filterMap[key]));
    const itemMap: Partial<Record<keyof U, T>> = {};

    for (const item of items) {
        const matchedFilter = Array.from(filters).find(([key, filterFn]) => {
            return filterFn(item);
        })
        if (matchedFilter) {
            const key = matchedFilter[0];
            itemMap[key] = item;
            filters.delete(key);
        }
    }
    return itemMap;
}


const items = [{ type: 'cool' }, { type: 'hot' }];
const mapped = filterMap(items, {
    cool: (item) => item.type === 'cool',
    hot: (item) => item.type === 'hot';
});

// mapped.hot, mapped.cool are type checked & typeahead completed by typescript
console.log(mapped.hot);
console.log(mapped.cool);