Converts array of objects to object with key

arrayToKeyedObject.spec.ts

describe('arrayToKeyedObject', () => {
  it('should return empty object if array are empty', () => {
    type GenericItems = { code: string }
    const items: GenericItems[] = []
    const result = arrayToKeyedObject(items, (item) => item.code)

    expect(result).toEqual({})
  })

  it('should return keyed object', () => {
    const items = [{ code: 'one' }, { code: 'two' }]
    const result = arrayToKeyedObject(items, (item) => item?.code)

    expect(result).toEqual({
      one: { code: 'one' },
      two: { code: 'two' }
    })
  })
})

arrayToKeyedObject.ts

function arrayToKeyedObject<T, K extends string>(
  array: T[],
  attributeGetter: (item: T) => K
) {
  if (!Array.isArray(array)) {
    throw new TypeError('First argument must be an array')
  }

  if (!attributeGetter || typeof attributeGetter !== 'function') {
    throw new TypeError('attributeGetter argument must me a function')
  }

  if (array.length === 0) {
    return {} as Record<K, T>
  }

  const map = {} as Record<K, T>

  for (const value of array) {
    const key = attributeGetter(value)
    map[key] = value
  }

  return map
}