CFP - Docs - pKeepWhen

pKeepWhen

(predicate: AsyncPredicate) => async (collection: Collection) => Collection

Keep entries that pass an asynchronous condition.

The predicate is called for all entries at once. See Notes for an example.

Try It

const gt2 = async n => n > 2
const keepWhenGt2 = pKeepWhen(gt2)

const arr = [4, 1, 3, 2]
await keepWhenGt2(arr) // is [4, 3]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await keepWhenGt2(obj) // is { d: 4, c: 3 }
const gt2 = async (n: number) => n > 2
const keepWhenGt2 = pKeepWhen(gt2)

const arr = [4, 1, 3, 2]
await keepWhenGt2(arr) // is [4, 3]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await keepWhenGt2(obj) // is { d: 4, c: 3 }

Try It

const gt2 = async n => n > 2
const keepWhenGt2 = pKeepWhen(gt2)

const arr = [4, 1, 3, 2]
await keepWhenGt2(arr) // is [4, 3]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await keepWhenGt2(obj) // is { d: 4, c: 3 }
const gt2 = async (n: number) => n > 2
const keepWhenGt2 = pKeepWhen(gt2)

const arr = [4, 1, 3, 2]
await keepWhenGt2(arr) // is [4, 3]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await keepWhenGt2(obj) // is { d: 4, c: 3 }

Sometimes we want to keep entries that pass an asynchronous condition. Below, we call a mock store API to see which items in our shopping cart give us rewards.

Try It

const mockStoreApi = {
  includedInRewards: async item => item.name === 'detergent',
}

const shoppingCart = [
  { name: 'broom', cost: 3 },
  { name: 'mop', cost: 10 },
  { name: 'detergent', cost: 13 },
]
const keepRewardItems = pKeepWhen(mockStoreApi.includedInRewards)

const rewardItems = await keepRewardItems(shoppingCart)

console.log('items gaining you rewards: ', rewardItems)
// prints
// items gaining you rewards:
// [{
//   name: detergent
//   cost: 13
// }]
type Item = {
  name: string
  cost: number
}

const mockStoreApi = {
  includedInRewards: async (item: Item) => item.name === 'detergent',
}

const shoppingCart: Item[] = [
  { name: 'broom', cost: 3 },
  { name: 'mop', cost: 10 },
  { name: 'detergent', cost: 13 },
]
const keepRewardItems = pKeepWhen(mockStoreApi.includedInRewards)<Item[]>

const rewardItems = await keepRewardItems(shoppingCart)

console.log('items gaining you rewards: ', rewardItems)
// prints
// items gaining you rewards:
// [{
//   name: detergent
//   cost: 13
// }]

Try It

const mockStoreApi = {
  includedInRewards: async item =>
    item.name === 'detergent',
}

const shoppingCart = [
  { name: 'broom', cost: 3 },
  { name: 'mop', cost: 10 },
  { name: 'detergent', cost: 13 },
]
const keepRewardItems = pKeepWhen(
  mockStoreApi.includedInRewards
)

const rewardItems =
  await keepRewardItems(shoppingCart)

console.log(
  'items gaining you rewards: ',
  rewardItems
)
// prints
// items gaining you rewards:
// [{
//   name: detergent
//   cost: 13
// }]
type Item = {
  name: string
  cost: number
}

const mockStoreApi = {
  includedInRewards: async (item: Item) =>
    item.name === 'detergent',
}

const shoppingCart: Item[] = [
  { name: 'broom', cost: 3 },
  { name: 'mop', cost: 10 },
  { name: 'detergent', cost: 13 },
]
const keepRewardItems = pKeepWhen(
  mockStoreApi.includedInRewards
)<Item[]>

const rewardItems =
  await keepRewardItems(shoppingCart)

console.log(
  'items gaining you rewards: ',
  rewardItems
)
// prints
// items gaining you rewards:
// [{
//   name: detergent
//   cost: 13
// }]

pKeepWhen calls the predicate for all entries at once. See async.filterLimit if you want to limit the concurrency.

Try It

const start = new Date().getTime()

const gt2 = async n => {
  const msPassed = Date.now() - start
  console.log(`ms passed: ${msPassed}, for n = ${n}`)

  await pWaitMs(20)
  return n > 2
}
const keepWhenGt2 = pKeepWhen(gt2)

await keepWhenGt2([2, 3, 4])
const totalMsPassed = Date.now() - start
console.log(`total ms passed: ${totalMsPassed}`)
const start = new Date().getTime()

const gt2 = async (n: number) => {
  const msPassed = Date.now() - start
  console.log(`ms passed: ${msPassed}, for n = ${n}`)

  await pWaitMs(20)
  return n > 2
}
const keepWhenGt2 = pKeepWhen(gt2)<number[]>

await keepWhenGt2([2, 3, 4])
const totalMsPassed = Date.now() - start
console.log(`total ms passed: ${totalMsPassed}`)

Try It

const start = new Date().getTime()

const gt2 = async n => {
  const msPassed = Date.now() - start
  console.log(
    `ms passed: ${msPassed}, for n = ${n}`
  )

  await pWaitMs(20)
  return n > 2
}
const keepWhenGt2 = pKeepWhen(gt2)

await keepWhenGt2([2, 3, 4])
const totalMsPassed = Date.now() - start
console.log(`total ms passed: ${totalMsPassed}`)
const start = new Date().getTime()

const gt2 = async (n: number) => {
  const msPassed = Date.now() - start
  console.log(
    `ms passed: ${msPassed}, for n = ${n}`
  )

  await pWaitMs(20)
  return n > 2
}
const keepWhenGt2 = pKeepWhen(gt2)<number[]>

await keepWhenGt2([2, 3, 4])
const totalMsPassed = Date.now() - start
console.log(`total ms passed: ${totalMsPassed}`)