CFP - Docs - getValueAtMapKey

getValueAtMapKey

(key: any) => (aMap: map) => Value | undefined

Return the value found at the map's key

Try It

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
const getA = getValueAtMapKey('a')
getA(aMap) // is 1

const emptyMap = new Map()
getA(emptyMap) // is undefined
const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
const getA = getValueAtMapKey('a')
getA(aMap) // is 1

const emptyMap = new Map()
getA(emptyMap) // is undefined

Try It

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
const getA = getValueAtMapKey('a')
getA(aMap) // is 1

const emptyMap = new Map()
getA(emptyMap) // is undefined
const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
const getA = getValueAtMapKey('a')
getA(aMap) // is 1

const emptyMap = new Map()
getA(emptyMap) // is undefined

Sometimes we need a map's value. Below, we're programming a new screen for New York metro (MTA) users. We need to display their balance and status. MTA stores data in separate tables with the person's object as the key. To test the screen, let's get Tom's data.

Try It

const tom = { first: 'tom', last: 'nelson' }
const ken = { first: 'ken', last: 'roberts' }
const chris = { first: 'chris', last: 'reyes' }

const metroBalance = new Map([
  [tom, '21.95'],
  [ken, '15.30'],
  [chris, '34.50'],
])

const metroSubscriptionStatus = new Map([
  [tom, 'active'],
  [ken, 'paused'],
  [chris, 'active'],
])

const metroData = {
  balance: metroBalance,
  status: metroSubscriptionStatus,
}

const getTomsValue = getValueAtMapKey(tom)
const getTomsData = mapValues(getTomsValue)
const tomsData = getTomsData(metroData)

console.log(tomsData)
// is {
//   balance: 21.95
//   status: active
// }
type Person = { first: string; last: string }

const tom: Person = { first: 'tom', last: 'nelson' }
const ken: Person = { first: 'ken', last: 'roberts' }
const chris: Person = { first: 'chris', last: 'reyes' }

const metroBalance = new Map([
  [tom, '21.95'],
  [ken, '15.30'],
  [chris, '34.50'],
])

const metroSubscriptionStatus = new Map([
  [tom, 'active'],
  [ken, 'paused'],
  [chris, 'active'],
])

type MetroData = {
  balance: Map<Person, string>
  status: Map<Person, string>
}
const metroData: MetroData = {
  balance: metroBalance,
  status: metroSubscriptionStatus,
}

const getTomsValue = getValueAtMapKey(tom)<string>
const getTomsData = mapValues(getTomsValue)<MetroData>
const tomsData = getTomsData(metroData)

console.log(tomsData)
// is {
//   balance: 21.95
//   status: active
// }

Try It

const tom = { first: 'tom', last: 'nelson' }
const ken = { first: 'ken', last: 'roberts' }
const chris = { first: 'chris', last: 'reyes' }

const metroBalance = new Map([
  [tom, '21.95'],
  [ken, '15.30'],
  [chris, '34.50'],
])

const metroSubscriptionStatus = new Map([
  [tom, 'active'],
  [ken, 'paused'],
  [chris, 'active'],
])

const metroData = {
  balance: metroBalance,
  status: metroSubscriptionStatus,
}

const getTomsValue = getValueAtMapKey(tom)
const getTomsData = mapValues(getTomsValue)
const tomsData = getTomsData(metroData)

console.log(tomsData)
// is {
//   balance: 21.95
//   status: active
// }
type Person = { first: string; last: string }

const tom: Person = {
  first: 'tom',
  last: 'nelson',
}
const ken: Person = {
  first: 'ken',
  last: 'roberts',
}
const chris: Person = {
  first: 'chris',
  last: 'reyes',
}

const metroBalance = new Map([
  [tom, '21.95'],
  [ken, '15.30'],
  [chris, '34.50'],
])

const metroSubscriptionStatus = new Map([
  [tom, 'active'],
  [ken, 'paused'],
  [chris, 'active'],
])

type MetroData = {
  balance: Map<Person, string>
  status: Map<Person, string>
}
const metroData: MetroData = {
  balance: metroBalance,
  status: metroSubscriptionStatus,
}

const getTomsValue = getValueAtMapKey(tom)<string>
const getTomsData = mapValues(
  getTomsValue
)<MetroData>
const tomsData = getTomsData(metroData)

console.log(tomsData)
// is {
//   balance: 21.95
//   status: active
// }