JSFiddle - React, Tailwind, and code Playground

JavaScript

function Something()
    {
        this.constructed;

        if (Something.prototype.isPrototypeOf(this) && !this.constructed)
        {
            alert("called as a c'tor"); this.constructed = true;
        }
        else
        {
            alert("called as a function");
        }
    }

    Something();              // "called as a function"
    new Something();          // "called as a c'tor"

    var x = new Something();  // "called as a c'tor"
    x.func = Something;
    x.func();                 // "called as a function"