can we define new properties on a object in javascript code example

Example 1: how to add property to object in javascript

var data = {
    'PropertyA': 1,
    'PropertyB': 2,
    'PropertyC': 3
};

data["PropertyD"] = 4;

// dialog box with 4 in it
alert(data.PropertyD);
alert(data["PropertyD"]);

Example 2: object object javascript

person = {
    'name':'john smith'
    'age':41
};

console.log(person);
//this will return [object Object]
//use
console.log(JSON.stringify(person));
//instead