CFP - Docs - forEach

forEach

(fn: Function) => (collection: Collection) => Collection

Call a function for each entry in collection

Try It

const logEntry = (val, key) => console.log(`${key}: ${val}`)
const logEach = forEach(logEntry)
logEach([1, 2, 3])
// is
// 0: 1
// 1: 2
// 2: 3

logEach({ a: 1, b: 2, c: 3 })
// is
// a: 1
// b: 2
// c: 3
const logEntry = (val: unknown, key: unknown) => console.log(`${key}: ${val}`)
const logEach = forEach(logEntry)
logEach([1, 2, 3])
// is
// 0: 1
// 1: 2
// 2: 3

logEach({ a: 1, b: 2, c: 3 })
// is
// a: 1
// b: 2
// c: 3

Try It

const logEntry = (val, key) =>
  console.log(`${key}: ${val}`)
const logEach = forEach(logEntry)
logEach([1, 2, 3])
// is
// 0: 1
// 1: 2
// 2: 3

logEach({ a: 1, b: 2, c: 3 })
// is
// a: 1
// b: 2
// c: 3
const logEntry = (val: unknown, key: unknown) =>
  console.log(`${key}: ${val}`)
const logEach = forEach(logEntry)
logEach([1, 2, 3])
// is
// 0: 1
// 1: 2
// 2: 3

logEach({ a: 1, b: 2, c: 3 })
// is
// a: 1
// b: 2
// c: 3

Sometimes we need to call a function for each item in a collection. Below, we are running a social media site. We track when people appear in search results to monitor trends. Let's update our database with two recent searches.

Try It

const searchResults1 = ['chris', 'liz', 'phil']
const searchResults2 = ['chris', 'liz']

const db = {
  searchResultsByName: {},
}

const incrementSearchResult = name => {
  if (db.searchResultsByName[name] === undefined) {
    db.searchResultsByName[name] = 0
  }
  db.searchResultsByName[name] += 1
}

const incrementResults = forEach(incrementSearchResult)

incrementResults(searchResults1)
incrementResults(searchResults2)

console.log(db.searchResultsByName)
// is {
//   chris: 2
//   liz: 2
//   phil: 1
// }
const searchResults1 = ['chris', 'liz', 'phil']
const searchResults2 = ['chris', 'liz']

const db = {
  searchResultsByName: {} as Record<string, number | undefined>,
}

const incrementSearchResult = (name: string) => {
  if (db.searchResultsByName[name] === undefined) {
    db.searchResultsByName[name] = 0
  }
  db.searchResultsByName[name] += 1
}

const incrementResults = forEach(incrementSearchResult)<string[]>

incrementResults(searchResults1)
incrementResults(searchResults2)

console.log(db.searchResultsByName)
// is {
//   chris: 2
//   liz: 2
//   phil: 1
// }

Try It

const searchResults1 = ['chris', 'liz', 'phil']
const searchResults2 = ['chris', 'liz']

const db = {
  searchResultsByName: {},
}

const incrementSearchResult = name => {
  if (
    db.searchResultsByName[name] === undefined
  ) {
    db.searchResultsByName[name] = 0
  }
  db.searchResultsByName[name] += 1
}

const incrementResults = forEach(
  incrementSearchResult
)

incrementResults(searchResults1)
incrementResults(searchResults2)

console.log(db.searchResultsByName)
// is {
//   chris: 2
//   liz: 2
//   phil: 1
// }
const searchResults1 = ['chris', 'liz', 'phil']
const searchResults2 = ['chris', 'liz']

const db = {
  searchResultsByName: {} as Record<
    string,
    number | undefined
  >,
}

const incrementSearchResult = (name: string) => {
  if (
    db.searchResultsByName[name] === undefined
  ) {
    db.searchResultsByName[name] = 0
  }
  db.searchResultsByName[name] += 1
}

const incrementResults = forEach(
  incrementSearchResult
)<string[]>

incrementResults(searchResults1)
incrementResults(searchResults2)

console.log(db.searchResultsByName)
// is {
//   chris: 2
//   liz: 2
//   phil: 1
// }

forEach is intended for side effects. If you're using this to modify the collection then you're likely misunderstanding Common FP. Please raise an issue so we can figure out a better approach for ya.