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['10'] = 'ten';
array['11'] = 'eleven';
array['12'] = 'twelve';

alert(Object.size(array));
alert(array['11']);