Lodash _.isFunction() Method

Beginner
5 min read
Updated: Nov 2026
5 examples
Lang
Decorative image with the word ISFUNCTION

Definition

Checks if value is classified as a Function object. Callables pass; RegExp and plain objects do not. Since Lodash 0.1.0.

Pass the value you want to inspect or convert. Read the return type carefully before you use the result.

Syntax

Call _.isFunction. Start with this line.

Lodash
_.isFunction(value)
CallWhat it does
_.isFunction(value)Primary signature.

Prefer import isFunction from "lodash/isFunction" when you want a smaller bundle.

Library declarations
Lodash
_.isFunction(value)

Parameters

ParameterDescription
valueRequired. The value to check

Return Value

Return ValueDescription
*true if Function object, else false

Lodash Examples

Example 1 — Official: Lodash vs RegExp

The library object is a function; a regex is not.

Lodash
_.isFunction(_);
// → true

_.isFunction(/abc/);
// → false
Try It Yourself

How It Works

  1. _ is the Lodash function object.
  2. isFunction sees a Function tag → true.
  3. /abc/ is a RegExp → different tag → false.
  4. Lesson. Callable ≠ “looks like a pattern object.”

Example 2 — Declarations, Arrows, and Classes

Common callable shapes all return true.

Lodash
function greet() {}
var arrow = () => {};
class Person {}

_.isFunction(greet);
// → true

_.isFunction(arrow);
// → true

_.isFunction(Person);
// → true
Try It Yourself

How It Works

  1. greet is a classic function declaration.
  2. arrow is still a Function object.
  3. Person is a class constructor — callable → true.
  4. Note. Instances (new Person()) are objects, not functions.

Example 3 — Async and Generator Functions

Modern function kinds still count as functions.

Lodash
async function load() {}
function* gen() { yield 1; }

_.isFunction(load);
// → true

_.isFunction(gen);
// → true

_.isFunction(gen());
// → false  // the iterator object, not the function
Try It Yourself

How It Works

  1. async function has an AsyncFunction tag → true.
  2. function* has a GeneratorFunction tag → true.
  3. gen() returns an iterator object → false.
  4. Tip. Check the function, not the result of calling it.

Example 4 — Non-Functions

Objects, strings, and null are not callables.

Lodash
_.isFunction({});
// → false

_.isFunction("fn");
// → false

_.isFunction(null);
// → false

_.isFunction(Math);
// → false  // object with methods, not a function itself
Try It Yourself

How It Works

  1. Plain object / string / null lack Function tags.
  2. Math is an object namespace — check Math.max instead.
  3. All four return false.
  4. Guard before calling optional callbacks.

Example 5 — Optional Callback Guard

Invoke a hook only when it is actually a function.

Lodash
function run(onReady) {
  if (_.isFunction(onReady)) {
    return onReady("ok");
  }
  return "skipped";
}

run(function (msg) { return "got " + msg; });
// → "got ok"

run(null);
// → "skipped"
Try It Yourself

How It Works

  1. isFunction guards the call site.
  2. Real callback runs and returns a string.
  3. null fails the check → default path.
  4. Use case. Options APIs with optional hooks.
Compatibility

Browser & Runtime Support

_.isFunction is a Lodash Lang helper (since 0.1.0). It runs anywhere Lodash 4.x runs — modern browsers (CDN or bundle) and Node.js / Bun / Deno with npm install lodash.

✓ Stable · Lodash 0.1.0+

_.isFunction()

Available in [email protected] full builds and the lodash/isFunction modular import. Works in evergreen browsers and current Node LTS when Lodash is installed.

100% With Lodash 4.x
Google Chrome Supported · Desktop & Mobile
Full support
Mozilla Firefox Supported · Desktop & Mobile
Full support
Apple Safari Supported · macOS & iOS
Full support
Microsoft Edge Supported · Chromium
Full support
Internet Explorer No native support · Use a polyfill
Polyfill
Opera Supported · Modern versions
Full support
Samsung Internet Supported · Android
Full support
Bun Supported · JavaScript runtime
Supported
Deno Supported · JavaScript runtime
Supported
Node.js Supported · Server runtime
Supported
Android WebView Supported · Modern WebView
Full support
_.isFunction Lodash 0.1.0+

Bottom line: Safe for production once Lodash is loaded. Prefer import isFunction from "lodash/isFunction". typeof value === "function" is a fine native alternative for most apps.

Frequently Asked Questions

_.isFunction(value) returns true if value is classified as a Function object, otherwise false.
Yes. Arrows, async functions, and generators are all treated as functions.
A class declaration creates a callable constructor function, so Lodash returns true.
No. _.isFunction(/abc/) is false — that is the official contrast example.
They usually agree. Lodash uses internal tags for consistent classification across engines and function kinds.
Use import isFunction from "lodash/isFunction" or require("lodash/isFunction") for tree-shaking. Full build: import _ from "lodash" then _.isFunction.

Next: _.isInteger()

Check whether a value is an integer.

_.isInteger() tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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