Prioritise a nested array of items

prioritise.ts

// From: https://twitter.com/rauschma/status/1487086371760136195?s=20&t=z_0I28Cjhgn1igKt90qmrw
import assert from 'assert/strict';

interface Character {
  name: string;
}

interface PrioritisedItem {
  name: string;
  priority: number;
}

const prios: Character[][] = [
  [{ name: "Jane" }, { name: "Tarzan" }],
  [{ name: "Cheetah" }],
];

const prioResult: PrioritisedItem[] = [
  { name: "Jane", priority: 1 },
  { name: "Tarzan", priority: 1 },
  { name: "Cheetah", priority: 2 },
];

const formatPrios = (data: Character[][]): PrioritisedItem[] =>
  data.reduce(
    (
      acc: PrioritisedItem[],
      curr: Character[],
      idx: number
    ): PrioritisedItem[] => {
      const remapped: PrioritisedItem[] = curr.map(
        (item: Character): PrioritisedItem => ({ ...item, priority: idx + 1 })
      );

      return [...acc, ...remapped];
    },
    []
  );

assert.deepEqual(
  prioResult,
  formatPrios(prios)
);