@zerodep/is.function NPM

@zerodep/is.function

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A utility to determine if a value is a function.

tl;dr

A short explanation / quick reference:

import { isFunction } from '@zerodep/is.function';

isFunction(() => {}); // true
isFunction('a string'); // false

Install

This utility is available from multiple @zerodep packages, enabling developers to select the most appropriately sized package (for both kb and capability) for different use cases. We believe one size does not fit all or most. See @zerodep/app, @zerodep/utils and @zerodep/is.

For Server & Build Tooling

For Node, or when compiling via babel, rollup, swc, tsc, webpack, etc... these are the instructions for you.

// all @zerodep features, capabilities and utilities
npm install @zerodep/app

// entire set of @zerodep utilities
npm install @zerodep/utils

// all @zerodep "is" utilities
npm install @zerodep/is

// only the is.function utility
npm install @zerodep/is.function

Of course, you may use yarn, pnpm, or the package manager of your choice. Only npm examples are shown for brevity.

Browser Direct

If you are using the script directly in a browser via a <script> tag or importing it into your own scripts, these are the instructions for you. We support both ESM and UMD formats.

<!-- for ES Modules (ESM) -->
<script type="module">
  import { isFunction } from 'https://cdn.jsdelivr.net/npm/@zerodep/is.function/esm.js';
  // ...your code here
</script>

<!--  OR  -->

<!--  for Universal Modules (UMD) - all @zerodep functions are in the global "zd" namespace -->
<script src="https://cdn.jsdelivr.net/npm/@zerodep/is.function/umd.js"></script>
<script>
  // example of "zd" prefix
  const result = zd.isFunction(() => {});
</script>

This package may be found on both jsDelivr and unpkg in UMD, ESM and CJS formats.

How to Use

This package exports the following:

Functions
- isFunction - a function to test if a provided value is a function

Signature

// typescript declaration
declare const isFunction: (value: any) => boolean;

Examples

All examples assume ESM or CJS packages. If using a UMD package remember to prefix with the zd namespace, e.g. zd.isFunction(...).

// import from the most appropriate @zerodep package for your needs / specific use case (see the Install section above)
import { isFunction } from '@zerodep/is.function';

isFunction(() => {}); // true
isFunction(class MyClass {}); // true <-- CAUTION

// strings
isFunction(''); // false
isFunction('a string'); // false

// integers
isFunction(42); // false
isFunction(3e8); // false

// floats
isFunction(-273.15); // false
isFunction(Math.PI); // false

// number-ish
isFunction(Number.POSITIVE_INFINITY); // false
isFunction(NaN); // false

// bigints
isFunction(8675309n); // false

// object literals
isFunction({}); // false
isFunction({ a: 'one', b: 'two' }); // false

// arrays
isFunction([]); // false
isFunction([1, 2, 3]); // false
isFunction(['a', 'b', 'c']); // false

// booleans
isFunction(true); // false
isFunction(false); // false

// other
isFunction(/^$\d{7}/g); // false
isFunction(new Date()); // false
isFunction(new Date('2022-02-24')); // false
isFunction(new Set()); // false
isFunction(new Set([1, 2, 3])); // false
isFunction(new Map()); // false
isFunction(new Map([['a', 1]])); // false
isFunction(Symbol()); // false
isFunction(new Error()); // false

// nothing
isFunction(null); // false
isFunction(undefined); // false

Related Packages

The following @zerodep packages may be helpful or more appropriate for your specific case:

@zerodep/guard.function - only allows float values (throws an error for non-function values), reduces the need to write if/else code

Advantages of @zerodep Packages

We help make source code more readable, more secure, faster to craft, less likely to have hidden defects, and easier to maintain.

Zero npm dependencies - completely eliminates all risk of supply-chain attacks, decreases node_modules folder size
Fully typed - typescript definitions are provided for every package for a better developer experience
Semantically named - package and method names are easy to grok, remember, use, and read
Documented - actually useful documentation with examples and helpful tips
Intelligently Packaged - multiple npm packages of different sizes available allowing a menu or a-la-carte composition of capabilities
100% Tested - all methods and packages are fully unit tested
ESM & CJS - has both ecmascript modules and common javascript exports, both are fully tree-shakable
CDN Available - available on fast content delivery networks in UMD, CJS and ESM formats
FP Inspired - gently opinionated to encourage functional programming style for cleaner and more maintainable software
Predictably Versioned - semantically versioned for peace-of-mind upgrading, this includes changelogs
MIT Licensed - permissively licensed for maximum usability

Support

All @zerodep packages are built for the ES2020 specification. Should you need to support older environments you will need to add appropriate polyfills. All packages are tested on the following platforms/browsers:

Browsers

Chrome - last 2 major versions
Firefox - last 2 major versions
Safari - last 2 major versions
Edge - last 2 major versions
Android - last 2 major versions
iOS - last 2 major versions

Node

v16.x - Gallium LTS
v14.x - Fermium LTS

It is likely the package will work on other technologies and version, however development and testing effort is only spent on the above.

Semver

All @zerodep packages, including this one, adhere to Semantic Versioning practices:

major versions: correlates with breaking changes to one or more method signatures
minor versions: includes addition of new functionality or backwards-compatible software improvements
patch versions: are reserved for copy changes, documentation enhancements and bug fixes

The above said, a security best practice is to pin your software packages to specific versions and only upgrade to more recent releases after careful inspection of any CHANGELOG, release notes and all software changes.