Node js check if a var is a function

Question

Possible Duplicate:
How can I check if a javascript variable is function type?

How i check if a variable is a function for Array exist Array.isArray() but Function.isFunction dos'nt exist

Worth mentioning that the accepted/best answer here is simpler than the referenced question, as this is just for node ( no compatibility issues ) — Adam Tolley, Aug 08 '16 at 23:52

score 48 · Accepted Answer · edited Feb 12 '18 at 15:41

48

if (typeof variable === 'function') {
    // do something
}

edited Feb 12 '18 at 15:41

аlex

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answered Oct 24 '12 at 16:46

paul

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`typeof class A {} === "function"` is `true`. – Frederik Krautwald Sep 16 '21 at 13:53

score 6 · Answer 2 · answered Oct 24 '12 at 16:50

6

You can use the instanceof operator.

var fn = function() {};
var result = fn instanceof Function; // result will be true

It also respects prototypal inheritance.

answered Oct 24 '12 at 16:50

Manu Clementz

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score 4 · Answer 3 · answered Oct 24 '12 at 17:24

4

Underscore.js is a library that has a lot of useful helpers, like the one you're looking for.

http://underscorejs.org/

_ = require('underscore');

var aFunction = function() { };
var notFunction = 'Not a function';

_.isFunction(aFunction); // true
_.isFunction(notFunction); // false

answered Oct 24 '12 at 17:24

BadCanyon

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I wouldn't use underscore for this case, given that the _.isFunction function is just `typeof obj == 'function' || false` - https://github.com/jashkenas/underscore/blob/e944e0275abb3e1f366417ba8facb5754a7ad273/underscore.js#L1338 – tylucaskelley Aug 09 '17 at 20:32

score 1 · Answer 4 · answered Oct 24 '12 at 17:04

var fn = function() {},
    toString = Object.prototype.toString;

first way:

if( toString.call( function(){} ) === '[object Function]' ) {
    //if is Function do something...
}

second way:

if( fn.constructor.name = 'Function' ) {
    //if is Function do something...
}

Hope it helps cheers:)!

Node js check if a var is a function

4 Answers4