CFP - Docs - pPassThrough

pPassThrough

async (value: any, fnArray: async function[]) => Result

Pass a value through asynchronous functions, returning the result.

Each function takes the result of the prior function as its parameter.

Try It

const increment = async n => n + 1
const double = async n => n * 2
const toAnswer = async n => 'answer: ' + n

const result1 = await pPassThrough(1, [increment, double, toAnswer])
console.log(result1) // is 'answer: 4'

const result2 = await pPassThrough(1, [])
console.log(result2) // is 1
const increment = async (n: number) => n + 1
const double = async (n: number) => n * 2
const toAnswer = async (n: number) => 'answer: ' + n

const result1 = await pPassThrough(1, [increment, double, toAnswer])
console.log(result1) // is 'answer: 4'

const result2 = await pPassThrough(1, [])
console.log(result2) // is 1

Try It

const increment = async n => n + 1
const double = async n => n * 2
const toAnswer = async n => 'answer: ' + n

const result1 = await pPassThrough(1, [
  increment,
  double,
  toAnswer,
])
console.log(result1) // is 'answer: 4'

const result2 = await pPassThrough(1, [])
console.log(result2) // is 1
const increment = async (n: number) => n + 1
const double = async (n: number) => n * 2
const toAnswer = async (n: number) =>
  'answer: ' + n

const result1 = await pPassThrough(1, [
  increment,
  double,
  toAnswer,
])
console.log(result1) // is 'answer: 4'

const result2 = await pPassThrough(1, [])
console.log(result2) // is 1

Sometimes we want to pass a value through asynchronous functions to process a result. Below, we're coding the checkout stage to our online shop. Let's first call the API to assign our shipping amount, then finalize the total.

Try It

const mockSalesTax = 0.08
const mockShipping = 10

const mockStoreApi = {
  assignShipping: async order => ({
    ...order,
    shipping: mockShipping,
  }),
  finalizeTotal: async order => ({
    ...order,
    salesTax: mockSalesTax,
    total: order.subtotal * (1 + mockSalesTax) + order.shipping,
  }),
}

const userLocation = 'cleveland'
const shoppingCart = ['broom', 'mop', 'detergent']
const order = {
  cart: shoppingCart,
  destination: userLocation,
  subtotal: 26,
}
const updatedOrder = await pPassThrough(order, [
  mockStoreApi.assignShipping,
  mockStoreApi.finalizeTotal,
])

console.log(updatedOrder)
// prints
// {
//   cart: [broom, mop, detergent]
//   destination: cleveland
//   subtotal: 26
//   shipping: 10
//   salesTax: 0.08
//   total: 38.08
// }
type Order = {
  cart: string[]
  destination: string
  salesTax: number
  shipping: number
  subtotal: number
  total: number
}

const mockSalesTax = 0.08
const mockShipping = 10

const mockStoreApi = {
  assignShipping: async (order: Order): Promise<Order> => ({
    ...order,
    shipping: mockShipping,
  }),
  finalizeTotal: async (order: Order): Promise<Order> => ({
    ...order,
    salesTax: mockSalesTax,
    total: order.subtotal * (1 + mockSalesTax) + order.shipping,
  }),
}

const userLocation = 'cleveland'
const shoppingCart = ['broom', 'mop', 'detergent']
const order = {
  cart: shoppingCart,
  destination: userLocation,
  subtotal: 26,
} as Order
const updatedOrder = await pPassThrough(order, [
  mockStoreApi.assignShipping,
  mockStoreApi.finalizeTotal,
])

console.log(updatedOrder)
// prints
// {
//   cart: [broom, mop, detergent]
//   destination: cleveland
//   subtotal: 26
//   shipping: 10
//   salesTax: 0.08
//   total: 38.08
// }

Try It

const mockSalesTax = 0.08
const mockShipping = 10

const mockStoreApi = {
  assignShipping: async order => ({
    ...order,
    shipping: mockShipping,
  }),
  finalizeTotal: async order => ({
    ...order,
    salesTax: mockSalesTax,
    total:
      order.subtotal * (1 + mockSalesTax) +
      order.shipping,
  }),
}

const userLocation = 'cleveland'
const shoppingCart = ['broom', 'mop', 'detergent']
const order = {
  cart: shoppingCart,
  destination: userLocation,
  subtotal: 26,
}
const updatedOrder = await pPassThrough(order, [
  mockStoreApi.assignShipping,
  mockStoreApi.finalizeTotal,
])

console.log(updatedOrder)
// prints
// {
//   cart: [broom, mop, detergent]
//   destination: cleveland
//   subtotal: 26
//   shipping: 10
//   salesTax: 0.08
//   total: 38.08
// }
type Order = {
  cart: string[]
  destination: string
  salesTax: number
  shipping: number
  subtotal: number
  total: number
}

const mockSalesTax = 0.08
const mockShipping = 10

const mockStoreApi = {
  assignShipping: async (
    order: Order
  ): Promise<Order> => ({
    ...order,
    shipping: mockShipping,
  }),
  finalizeTotal: async (
    order: Order
  ): Promise<Order> => ({
    ...order,
    salesTax: mockSalesTax,
    total:
      order.subtotal * (1 + mockSalesTax) +
      order.shipping,
  }),
}

const userLocation = 'cleveland'
const shoppingCart = ['broom', 'mop', 'detergent']
const order = {
  cart: shoppingCart,
  destination: userLocation,
  subtotal: 26,
} as Order
const updatedOrder = await pPassThrough(order, [
  mockStoreApi.assignShipping,
  mockStoreApi.finalizeTotal,
])

console.log(updatedOrder)
// prints
// {
//   cart: [broom, mop, detergent]
//   destination: cleveland
//   subtotal: 26
//   shipping: 10
//   salesTax: 0.08
//   total: 38.08
// }

When to use pPassThrough vs. pCompose?
They can often be used interchangeably. Compose allows you to name a group of functions, which can sometimes be helpful. Other times a name is unnecessary, and you just want to pass data through.

When to use pPassThrough vs. pCompose?