Kyle Shevlin

const indexByKey = key => arr =>
  arr.reduce((acc, cur) => {
    acc[cur[key]] = cur
    return acc
  }, {})

Use this function to make look ups based on a key for an array of items O(1). So long as your list doesn’t change, you should only have to run this once.

Here’s an example:

const indexById = indexByKey('id')

const members = [
  { id: 1, name: 'Kyle' },
  { id: 2, name: 'Krios' }, // my cat
  { id: 3, name: 'Tali' }, //  my other cat
]

const membersById = indexById(members)
/*
  {
    '1': { id: 1, name: 'Kyle' },
    '2': { id: 2, name: 'Krios' },
    '3': { id: 3, name: 'Tali' }
  }
*/

Make sure the key you’re using is unique to each object, otherwise you’ll have an incorrect index due to key collisions.

Kyle Shevlin is the founder & lead software engineer of Agathist, a software development firm with a mission to build good software with good people.