is-async-function

Is function really asynchronous function? Trying to guess that based on check if common-callback-names exists as function arguments names or you can pass your custom.

Install

Install with npm

$ npm i is-async-function --save

Usage

For more use-cases see the tests

const isAsyncFunction = require('is-async-function')

API

isAsyncFunction

Trying to guess is fn asynchronous function or not. But not is-callback-function be aware of that diff.

Params

• fn {Function}: is this fn a callback function
• names {Array}: arguments names, default are common-callback-names
• strict {Boolean}: defaults to true to always return a boolean, pass false to get index (position) - this is useful when you wanna understand which "callback name" exists as argument in that fn
• returns {Boolean|Number}: always boolean true or false when on strict mode, othewise it can be Number index representing the position and if index is 0 it is transformed to boolean true - so always positive value if function is async.

Example

var fs = require('fs')
var isAsyncFn = require('is-async-function')

console.log(isAsyncFunction(fs.readFile)) // => true
console.log(isAsyncFunction(fs.stat)) // => true

console.log(isAsyncFunction(fs.readFileSync)) // => false
console.log(isAsyncFunction(fs.statSync)) // => false

// or pass custom names to recognize as `async`
console.log(isAsyncFunction(fs.stat, ['cb'])) // => false
console.log(isAsyncFunction(fs.readFile, ['foo', 'bar']))
// => false, because fs.readFile uses `cb`

non-strict mode

passing false as second or third argument

var isAsyncFunction = require('is-async-function')

console.log(isAsyncFunction(fs.readFile, false)) // => 2
// => 2, because it callback argument is called `cb`
// and that's the third element in `common-callback-names` array

console.log(isAsyncFunction(fs.stat, false)) // => 1
// => 1, because it callback argument is called `callback_`
// and that's the second element in `common-callback-names` array

Side note: In previous nodejs versions it was called in a few different ways - cb_, callback_ and etc. That's why common-callback-names exists. As in v7 it seems everything now is called callback. So in most of the cases you will get boolean true always - both in strict and non-strict mode. In non-strict mode that will mean your function has argument called callback.

If you pass array of names as second argument, in non-strict mode you will get index of that array.

Example

var isAsyncFn = require('is-async-function')

// you considered you callback fucntion
// to be called `qux` for some reason
function myAsyncFn (foo, bar, qux) {
  qux(null, 123)
}

console.log(isAsyncFn(myAsyncFn)) // => false
console.log(isAsyncFn(myAsyncFn, false)) // => false

console.log(isAsyncFn(myAsyncFn, ['callback', 'qux'], false)) // => 1
// you are getting "1", because `qux` is second item
// in provided `names` array.

Related

• common-callback-names: List of common callback names - callback, cb, callback_, next, done. | homepage
• fn-args: Get the arguments of a function | homepage
• fn-name: Get the name of a named function | homepage
• function-arguments: Get arguments of a function, useful for and used in dependency injectors… more | homepage
• get-fn-name: Get function name with strictness and correctness in mind. Also works for… more | homepage
• is-callback-function: Returns true if function is a callback. Checks its name is one… more | homepage
• parse-function: Parse a function, arrow function or string to object with name, args… more | homepage

Contributing

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.
But before doing anything, please read the CONTRIBUTING.md guidelines.

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