@arrows/array/src/groupBy_.test.ts

Functional tools for JS arrays

import { groupBy_ } from "./index"

describe("Array groupByX", () => {
  it("returns object that groups array elements by key calculated by grouping function", () => {
    const arr = [
      { type: "animal", name: "monkey" },
      { type: "plant", name: "oak" },
      { type: "animal", name: "elephant" },
      { type: "mineral", name: "quartz" },
    ]
    const groupingFn = (item) => item.type

    const result = groupBy_(groupingFn, arr)
    const result2 = groupBy_(groupingFn)(arr)

    const expected = {
      animal: [
        { type: "animal", name: "monkey" },
        { type: "animal", name: "elephant" },
      ],
      plant: [{ type: "plant", name: "oak" }],
      mineral: [{ type: "mineral", name: "quartz" }],
    }

    expect(result).toEqual(result2)
    expect(result).toEqual(expected)
  })

  it("returns empty object if empty array is provided", () => {
    const arr = []
    const groupingFn = (item) => item.type

    const result = groupBy_(groupingFn, arr)
    const result2 = groupBy_(groupingFn)(arr)
    const expected = {}

    expect(result).toEqual(result2)
    expect(result).toEqual(expected)
  })
})