magic-hook

Extends functions with pre hooks.

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magic-hook
Extends functions with pre hooks.

Build Status Coverage Status npm version

Installation

npm i -S magic-hook

Usage

You can add pre hooks to extend your methods.
'use strict'
var hook = require('magic-hook')

// The target function
function concat(a, b) {
  return a + b
}

// The hooked function
var hookedConcat = hook(concat)

// A pre hook
var msgNo = 0
function counterHook(next, a, b) {
  return next('concatenation #' + (++msgNo) + ': ' + a, b)
}
hookedConcat.pre(counterHook)

for (var i = 3; i--;) console.log(hookedConcat('Hello ', 'world!'))
//> concatenation #1: Hello world!
//> concatenation #2: Hello world!
//> concatenation #3: Hello world!

Hooks can be removed using removePre:
hookedConcat.removePre(counterHook)

console.log(hookedConcat('Hello ', 'world!'))
//> Hello world!

To remove all pres associated with a hook just call removePre with no arguments:
hookedConcat.removePre()

To abort the target function's execution just don't call the next function in the pre hook:
hookedConcat.pre(function(next) {
  return 'The original function was overwritten';
})

console.log(hookedConcat("Doesn't matter what goes here"))
//> The original function was overwritten

You can overwrite the target function's result as well:
var hookedSum = hook(function(a, b) { return a + b; })

hookedSum.pre(function(sum, a, b) {
  if (a === 1 && b === 1) return 3

  return sum(a, b)
})

console.log(hookedSum(2, 2))
//> 4

console.log(hookedSum(1, 1))
//> 3

Motivation

Suppose you have an object with a save method.
It would be nice to be able to declare code that runs before save. For example, you might want to run validation code before every save. Or you might want to create plugins that will modify the input parameters of your save method.

License

MIT © Zoltan Kochan