JSFiddle - React, Tailwind, and code Playground

JavaScript

function CustomElement() {
    var ele = document.createElement("input");
    ele.type = "button";
    ele.value = "Testing";
    // do stuff to ele
    ele.CustomProperty = {one:"two", three:"four"};
    
    ele.toString = function(){
        return '<input type="'+this.type+'" value="'+this.value+'" />';
    };
        
    return ele;
}

var tmp = CustomElement();

document.body.innerHTML += tmp;
tmp.id = "Test";
document.body.appendChild(tmp);

console.log(tmp.CustomProperty);
console.log(document.getElementById("Test").CustomProperty);