JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = { 'foo': true };

function Custom(obj) {
    for ( prop in obj ) {
        if ( obj.hasOwnProperty(prop) ) {
            this[prop] = obj[prop];
        }
    }
}

Custom.prototype.bar = true;

var obj2 = new Custom(obj);

document.write( obj2.foo );
document.write( obj2.bar );