CFP - Docs - pDiscardWhen

pDiscardWhen

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

Discard 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 discardWhenGt2 = pDiscardWhen(gt2)

const arr = [4, 1, 3, 2]
await discardWhenGt2(arr) // is [1, 2]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await discardWhenGt2(obj) // is { a: 1, b: 2 }
const gt2 = async (n: number) => n > 2
const discardWhenGt2 = pDiscardWhen(gt2)

const arr = [4, 1, 3, 2]
await discardWhenGt2(arr) // is [1, 2]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await discardWhenGt2(obj) // is { a: 1, b: 2 }

Try It

const gt2 = async n => n > 2
const discardWhenGt2 = pDiscardWhen(gt2)

const arr = [4, 1, 3, 2]
await discardWhenGt2(arr) // is [1, 2]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await discardWhenGt2(obj) // is { a: 1, b: 2 }
const gt2 = async (n: number) => n > 2
const discardWhenGt2 = pDiscardWhen(gt2)

const arr = [4, 1, 3, 2]
await discardWhenGt2(arr) // is [1, 2]

const obj = { d: 4, a: 1, c: 3, b: 2 }
await discardWhenGt2(obj) // is { a: 1, b: 2 }

Sometimes we want to discard entries that pass an asynchronous condition. Below, we need to find the items in our shopping cart requiring a shipping fee. Let's call the mock store API to remove items in our shopping cart with free shipping.

Try It

const mockStoreApi = {
  hasFreeShipping: async item => item === 'detergent',
}

const shoppingCart = ['broom', 'mop', 'detergent']
const discardFreeShippingItems = pDiscardWhen(mockStoreApi.hasFreeShipping)

const itemsWithShippingCharge = await discardFreeShippingItems(shoppingCart)
console.log(itemsWithShippingCharge)
// is ['broom', 'mop']
const mockStoreApi = {
  hasFreeShipping: async (item: string) => item === 'detergent',
}

const shoppingCart = ['broom', 'mop', 'detergent']
const discardFreeShippingItems = pDiscardWhen(mockStoreApi.hasFreeShipping)<
  string[]
>

const itemsWithShippingCharge = await discardFreeShippingItems(shoppingCart)
console.log(itemsWithShippingCharge)
// is ['broom', 'mop']

Try It

const mockStoreApi = {
  hasFreeShipping: async item =>
    item === 'detergent',
}

const shoppingCart = ['broom', 'mop', 'detergent']
const discardFreeShippingItems = pDiscardWhen(
  mockStoreApi.hasFreeShipping
)

const itemsWithShippingCharge =
  await discardFreeShippingItems(shoppingCart)
console.log(itemsWithShippingCharge)
// is ['broom', 'mop']
const mockStoreApi = {
  hasFreeShipping: async (item: string) =>
    item === 'detergent',
}

const shoppingCart = ['broom', 'mop', 'detergent']
const discardFreeShippingItems = pDiscardWhen(
  mockStoreApi.hasFreeShipping
)<string[]>

const itemsWithShippingCharge =
  await discardFreeShippingItems(shoppingCart)
console.log(itemsWithShippingCharge)
// is ['broom', 'mop']

pDiscardWhen 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 discardWhenGt2 = pDiscardWhen(gt2)

await discardWhenGt2([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 discardWhenGt2 = pDiscardWhen(gt2)<number[]>

await discardWhenGt2([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 discardWhenGt2 = pDiscardWhen(gt2)

await discardWhenGt2([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 discardWhenGt2 = pDiscardWhen(gt2)<number[]>

await discardWhenGt2([2, 3, 4])
const totalMsPassed = Date.now() - start
console.log(`total ms passed: ${totalMsPassed}`)