wrappy

What is wrappy?

The wrappy npm package is a simple utility module designed to wrap asynchronous functions. It ensures that the callback provided to the wrapped function is only called once, which can be useful in preventing issues where a callback might accidentally be called multiple times due to programming errors.

What are wrappy's main functionalities?

Callback wrapping

This code demonstrates how to use wrappy to wrap a callback function so that it can only be called once. The 'once' function wraps the provided function 'fn' using wrappy, ensuring that subsequent calls to 'wrapped' after the first one have no effect.

const wrappy = require('wrappy')

function once (fn) {
  return wrappy(function () {
    if (fn === null) return
    var callFn = fn
    fn = null
    callFn.apply(this, arguments)
  })
}

var wrapped = once(function (a) {
  console.log('Called with', a)
})

wrapped('first call')
wrapped('second call') // This will not be called

Other packages similar to wrappy

once

The 'once' package is similar to wrappy in that it ensures a function can only be called once. It is more specialized than wrappy, as it is specifically designed for the purpose of creating functions that can only be called one time, whereas wrappy is a more general-purpose wrapper.

lodash.once

Provided by the popular Lodash utility library, 'lodash.once' is a function that ensures a given function can only be called once. Like 'once', it is more specialized compared to wrappy, and it comes with the additional overhead of the Lodash library if you are not already using it in your project.

README

wrappy

Callback wrapping utility

USAGE

var wrappy = require("wrappy")

// var wrapper = wrappy(wrapperFunction)

// make sure a cb is called only once
// See also: http://npm.im/once for this specific use case
var once = wrappy(function (cb) {
  var called = false
  return function () {
    if (called) return
    called = true
    return cb.apply(this, arguments)
  }
})

function printBoo () {
  console.log('boo')
}
// has some rando property
printBoo.iAmBooPrinter = true

var onlyPrintOnce = once(printBoo)

onlyPrintOnce() // prints 'boo'
onlyPrintOnce() // does nothing

// random property is retained!
assert.equal(onlyPrintOnce.iAmBooPrinter, true)