how not to use reduce

Why not reduce?

This list intend to be a forever growing one that hope to collect typical patterns of reduce to avoid. Please feel free to suggest more examples!

This post is not about space / time performance perks by not using reduce. This is all about readability.

🔴 Do not

faces.reduce((acc, face) => {
  return [...acc, mask(face)]
}, [])

✅ Do

faces.map(mask)

🔴 Do not

bags.reduce((acc, bag) => {
  return [...acc, ...bag.apples]
}, [])

✅ Do

bags.flatMap(bag => bag.apples)

🔴 Do not

phones.reduce((acc, phone) => {
  return isNew(phone) ? [...acc, phone] : acc
}, [])

✅ Do

phones.filter(isNew)

🔴 Do not

dogs.reduce((acc, dog) => {
  return isHappy(dog) ? acc + 1 : acc
}, 0)

✅ Do

dogs.filter(isHappy).length

🔴 Do not

people.reduce((acc, person) => ({
  [person.dna]: person
}), {})

✅ Do

Object.fromEntries(
  people.map(person => [person.dna, person])
)

🔴 Do not

people.reduce((acc, person) => {
  return Math.max(acc, person.age)
}, -Infinity)

✅ Do

Math.max(...people.map(person => person.age))