is-function

What is is-function?

The is-function npm package is a simple utility used for checking if a given value is a function. It is particularly useful in JavaScript environments where determining the type of an object can sometimes be less straightforward due to the dynamic nature of the language. This package provides a reliable way to ensure that a variable holds a function before attempting to invoke it, thus preventing runtime errors in code.

What are is-function's main functionalities?

Function Type Checking

This feature allows developers to check if a variable is a function. It supports various types of functions including regular functions, async functions, and arrow functions. It returns true if the variable is a function and false otherwise. This is particularly useful for validating callbacks or any variable that is expected to be a function before invoking it.

const isFunction = require('is-function');

console.log(isFunction(function() {})); // true
console.log(isFunction(async () => {})); // true
console.log(isFunction(() => {})); // true
console.log(isFunction(class MyClass {})); // false
console.log(isFunction({})); // false

Other packages similar to is-function

lodash.isfunction

lodash.isfunction is a part of the Lodash library, which is a broader utility library for JavaScript. While is-function focuses solely on checking if a value is a function, lodash.isfunction offers this functionality within the context of a larger set of utility functions. Lodash's isFunction method may be preferred in projects that already use Lodash for other utilities.

kind-of

kind-of is a more general type checking library that can determine the type of a given value, including whether it is a function. Unlike is-function, which is specialized for function type checking, kind-of can be used to check a wide variety of types such as strings, numbers, objects, etc. This makes kind-of a more versatile choice if your project requires extensive type checking beyond just functions.

README

is-function

Is that thing a function? Use this module to find out.

API

module.exports = function isFunction(fn) -> Boolean

Return true if fn is a function, otherwise false.

Why not typeof fn === 'function'

Because certain old browsers misreport the type of RegExp objects as functions.

Acknowledgements

I stole this from https://github.com/ljharb/object-keys

License

MIT