ID Map

id_map.ts

// id_map.ts
//
// Convert an array of objects T that have a string ID to a
// Record<string, T>.

export type Identifiable = {
  id: string;
};

export type IDMap<T> = {
  [key: string]: T;
};

export const toIDMap = <T extends Identifiable>(data: T[]) => {
  return data.reduce((acc, val) => {
    acc[val.id] = val;
    return acc;
  }, {} as IDMap<T>);
};

id_map_test.ts

import { toIDMap } from "./id_map";

interface Point {
  id: string;
  x: number;
  y: number;
}

it("converts an array of things to a Record dictionary", () => {
  const data: Point[] = [
    { id: "one", x: 10, y: 20 },
    { id: "two", x: 20, y: 40 },
    { id: "three", x: 30, y: 80 },
    { id: "two", x: 99, y: 999 }
  ];
  const xfm = toIDMap(data);
  expect(Object.keys(xfm).length).toBe(3);
  expect(xfm["one"].x).toBe(10);
  expect(xfm["two"].y).toBe(999); // because dupe keys not ok, this comes later
});