JSFiddle - React, Tailwind, and code Playground

JavaScript

var statics = (function() {
    var map = new WeakMap;
    return function(inst) {
        var ctor = inst.constructor;
        return map.get(ctor) || map.set(ctor, {});
    };
})();

var a = function() {};
var b = function() {};

var inst1 = new a;
var inst2 = new a;
var inst3 = new b;

statics(inst1).foo = 123;
statics(inst3).foo = 456;

console.log( statics(inst1).foo );
console.log( statics(inst2).foo );
console.log( statics(inst3).foo );