JSFiddle - React, Tailwind, and code Playground

JavaScript

Object.size = function(obj) {
    var size = 0,
        key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};

var array = [];
array["foo"] = "bar";
array["bar"] = "foo";

var size = Object.size(array);
document.write(size);