when to use `Record` in typescript

to quote WaterNinja101 from svelte discord:

Object.keys is defined to return a string[]

btw if you're curious why Object.keys(foo) returns string[] instead of keyof foo, it's because of this (ven)

const foo = {
  bar: 12,
  baz: 42
} as { bar: 12 } // okay cast

Object.keys(foo) // not actually keyof typeof foo, since it also contains baz

typescript doesn't care where that string[] came from, so when you iterate over it, it goes "hey, you can't use any string to access a property of this object"

a Record type specifically says "you can use any string to access a property on this object"

example of a record:

type roles = 'tester' | 'developer' | 'manager'

const staffCount: Record<roles, number> = {
	tester: 10,
	developer: 20,
	manager: 1
}

source (12ft'd medium article explaining more about the Record keyword)

when to use Record in typescript ​

when to use `Record` in typescript