prepost

Alter arguments and return values before and after a function is called

Install

npm install prepost

Usage

Alter arguments to a function:

import { pre } from 'prepost'

const add = (a, b) =>  a + b
const doubleAdd = pre((a, b) => [a * 2, b * 2], add)

add(1, 2) // -> 3
doubleAdd(1, 2) // -> 6

Alter return value from a function:

import { post } from 'prepost'

const add = (a, b) =>  a + b
const doubleAdd = post(add, res => res * 2)

add(1, 2) // -> 3
doubleAdd(1, 2) // -> 6

Async alter arguments:

import { pre } from 'prepost'

const add = (a, b) =>  a + b
const doubleAdd = pre(
  (a, b) => new Promise(resolve => setTimeout(resolve([a * 2, b * 2]), 1000)),
  add
)

add(1, 2) // -> 3
await doubleAdd(1, 2) // -> 6

Async alter return value:

import { post } from 'prepost'

const add = (a, b) =>  a + b
const doubleAdd = post(
  add,
  res => new Promise(resolve => setTimeout(resolve(res * 2), 1000))
)

add(1, 2) // -> 3
await doubleAdd(1, 2) // -> 6

API

pre(preFunc, [preFunc1, preFunc2, ...,] func)

• preFunc - function (or array of functions) to call before func. It is passed arguments as they would be if calling func normally. preFunc must return an array of arguments or a promise that resolves to an array.
• preFunc1, preFunc2, ... - other functions to call in series before func. The altered arguments from preFunc are passed to preFunc1 and so on.
• func - function to call after all the pre-functions have run and altered arguments

Returns a function that when called will call all the pre-functions in order before finally calling func.

NOTE: If any one of your pre functions returns a promise then the function returned by pre becomes async (returns a promise), regardless of whether func was already async or not.

post(func, postFunc [, postFunc1, postFunc2, ...])

• func - function to call and pass return value to postFunc
• postFunc - function (or array of functions) to call after func. It is passed the return value as it's first argument. If func returns a promise, this is first resolved before postFunc is called. preFunc should return the altered return value from func or a promise that resolves to the return value.
• postFunc1, postFunc2, ... - other functions to call in series after func. The altered return value from postFunc is passed to postFunc1 and so on.

Returns a function that when called will call all the post-functions in order after calling func.

NOTE: If any one of your post functions returns a promise then the function returned by post becomes async (returns a promise), regardless of whether func was already async or not.

Contribute

Feel free to dive in! Open an issue or submit PRs.

License

MIT © Alan Shaw