transforming-links.ts

const links = [
  { name: 'pablo', category: 'cat' },
  { name: 'harper', category: 'cat' },
  { name: 'phyllis', category: 'dog' },
  { name: 'derp', category: 'snake' },
]

// option 1: "oops, forgot the snakes"
const catLinks = []
const dogLinks = []

links.forEach(link => {
  if (link.category === 'cat') catLinks.push(link)
  if (link.category === 'dog') dogLinks.push(link)
})

// option 2: let's reduce 💪
const transformedGoal = {
  cat: [
    { name: 'pablo', category: 'cat' },
    { name: 'harper', category: 'cat' },
  ],
  dog: [
    { name: 'phyllis', category: 'dog' }
  ],
  snake: [
    { name: 'derp', category: 'snake' },
  ],
}

const transformed = links.reduce(
  (acc, link) => {
    acc[link.category] = [...acc[link.category], link]
    return acc
  },
  {} as Record<string, (typeof links[0])[]>
)

// @ts-expect-error didn't import it
assertDeepEqual(transformedGoal, transformed)