is-callable

What is is-callable?

The is-callable npm package is used to determine if a value is callable, meaning it can be called as a function. This is useful for type-checking in JavaScript where the typeof operator can be insufficient for certain cases, such as distinguishing between callable and non-callable objects.

What are is-callable's main functionalities?

Check if a value is callable

This feature allows you to check if various types of values are callable, including regular functions, async functions, arrow functions, and classes. It also correctly identifies non-callable objects like regex literals and plain objects.

const isCallable = require('is-callable');

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

Other packages similar to is-callable

is-function

The is-function package is similar to is-callable in that it checks if a given value is a function. However, it may not handle all the cases that is-callable does, such as ES6 classes or callable objects.

lodash.isfunction

Lodash provides a method called isFunction which is part of the larger lodash utility library. It is similar to is-callable but is part of a larger set of utility functions and may not distinguish between all types of callable entities as is-callable does.

README

is-callable

Is this JS value callable? Works with Functions and GeneratorFunctions, despite ES6 @@toStringTag.

Supported engines

Automatically tested in every minor version of node.

Manually tested in:

• Safari: v4 - v15 _{(4, 5, 5.1, 6.0.5, 6.2, 7.1, 8, 9.1.3, 10.1.2, 11.1.2, 12.1, 13.1.2, 14.1.2, 15.3, 15.6.1)}
  • Note: Safari 9 has class, but Function.prototype.toString hides that progeny and makes them look like functions, so class constructors will be reported by this package as callable, when they are not in fact callable.
• Chrome: v15 - v81, v83 - v106_{(every integer version)}
  • Note: This includes Edge v80+ and Opera v15+, which matches Chrome
• Firefox: v3, v3.6, v4 - v105 _{(every integer version)}
  • Note: v45 - v54 has class, but Function.prototype.toString hides that progeny and makes them look like functions, so class constructors will be reported by this package as callable, when they are not in fact callable.
  • Note: in v42 - v63, Function.prototype.toString throws on HTML element constructors, or a Proxy to a function
  • Note: in v20 - v35, HTML element constructors are not callable, despite having typeof function.
  • Note: in v19, document.all is not callable.
• IE: v6 - v11_{(every integer version}
• Opera: v11.1, v11.5, v11.6, v12.1, v12.14, v12.15, v12.16, v15+ _{v15+ matches Chrome}

Example

var isCallable = require('is-callable');
var assert = require('assert');

assert.notOk(isCallable(undefined));
assert.notOk(isCallable(null));
assert.notOk(isCallable(false));
assert.notOk(isCallable(true));
assert.notOk(isCallable([]));
assert.notOk(isCallable({}));
assert.notOk(isCallable(/a/g));
assert.notOk(isCallable(new RegExp('a', 'g')));
assert.notOk(isCallable(new Date()));
assert.notOk(isCallable(42));
assert.notOk(isCallable(NaN));
assert.notOk(isCallable(Infinity));
assert.notOk(isCallable(new Number(42)));
assert.notOk(isCallable('foo'));
assert.notOk(isCallable(Object('foo')));

assert.ok(isCallable(function () {}));
assert.ok(isCallable(function* () {}));
assert.ok(isCallable(x => x * x));

Install

Install with

npm install is-callable

Tests

Simply clone the repo, npm install, and run npm test

Changelog

v1.2.7 - 2022-09-23

Commits

• [Fix] recognize document.all in IE 6-10 06c1db2
• [Tests] improve logic for FF 20-35 0f7d9b9
• [Fix] handle document.all in FF 27 (and +, probably) 696c661
• [Tests] fix proxy tests in FF 42-63 985df0d
• [readme] update tested browsers 389e919
• [Fix] detect document.all in Opera 12.16 b9f1022
• [Fix] HTML elements: properly report as callable in Opera 12.16 17391fe
• [Tests] fix inverted logic in FF3 test 056ebd4