Alter arguments and return values before and after a function is called
npm install prepost  
> Alter arguments and return values before and after a function is called
``sh`
npm install prepost
Alter arguments to a function:
`js
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:
`js
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:
`js
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:
`js
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
`
#### 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
* - 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.
Feel free to dive in! Open an issue or submit PRs.
MIT © Alan Shaw