JSFiddle - React, Tailwind, and code Playground

JavaScript

(function() {
    constructors = {};
    window.findConstructorName = function(instance) {
        var constructor = instance.constructor;
        var name = constructors[constructor];
        if(name !== undefined) {
            return name;
        }
        
        var traversed = [];
        var nestedFind = function(root) {       
            if(typeof root == "function" || traversed[root]) {
                return       
            }
            
            traversed[root] = true;
            for(var index in root) {               
                if(root[index] == constructor) {
                    return index;
                }
                
                
                var found = nestedFind(root[index]);  
                if(found !== undefined) {
                    return found;
                }
            }
        }
            
        name = nestedFind(window);
        constructors[constructor] = name;
        return name;
    }
})();
                
var MyApp = {};
MyApp.Foo = function() {
};
        
var instance = new MyApp.Foo();
console.log(findConstructorName(instance));