How To Know If A Function Is A Class Or A Function

I'm actually trying to differentiate (in my code) functions and classes. I need to know, in a simple console.log, if the parameter of my function is a class or a simple function. I

Solution 1:

There aren't any classes in JavaScript. Though functions can be instanciated with the new keyword.

You can check if something is a function with instanceof:

var a = function() {};

a instanceofFunction; // true

An instanciated function will be an instance of that specific function:

var b = newa();

b instanceofFunction; // false
b instanceof a; // true

Solution 2:

There are no classes* in Javascript. Instead functions in JavaScript can act like constructors with the help of new keyword. (constructor pattern)

Objects in JavaScript directly inherit from other objects, hence we don't need classes. All we need is a way to create and extend objects.

You can use jQuery.isFunction() to check if the argument passed to isFunction() is a Javascript function object.

From the documentation:

jQuery.isFunction()

Description: Determine if the argument passed is a JavaScript function object.

EDIT: As rightly pointed out by user2867288, the statement that Javascript has no classes needs to be taken with a pinch of salt.

Read these articles for more information about the ECMAScript 6 standard:

• ECMAScript 6 Wiki
• Classes in ECMAScript 6

Solution 3:

Constructors ("classes") are only functions. There's not much that differentiates them.

However, their usage is quite different. Classes do typically have methods and maybe even other properties on their prototype. And that's in fact how you can distinguish them. Bound functions and functions constructed using arrow notation (ES6) even don't have a prototype at all.

functionisFunc(fn) {
    returntypeof fn == "function" && (!fn.prototype || !Object.keys(fn.prototype).length);
}

_{1: not detecting atypical classes that don't make use of prototypical inheritance}