JSFiddle - React, Tailwind, and code Playground
HTML
<input type='text' id='txtName' />
<button id='btnAddProperty'>Add</button>
JavaScript
var obj = {
"1":"aa",
"2":"bb"
};
var noOfItems=Object.keys(obj).length;
$('#btnAddProperty').on('click',function(){
noOfItems++;
obj[noOfItems]=$.trim($('#txtName').val());
console.log(obj);
});