Add new attribute (element) to JSON object using JavaScript

var jsonObj = {
    members: 
           {
            host: "hostName",
            viewers: 
            {
                user1: "value1",
                user2: "value2",
                user3: "value3"
            }
        }
}

var i;

for(i=4; i<=8; i++){
    var newUser = "user" + i;
    var newValue = "value" + i;
    jsonObj.members.viewers[newUser] = newValue ;

}

console.log(jsonObj);

A JSON object is simply a javascript object, so with Javascript being a prototype based language, all you have to do is address it using the dot notation.

mything.NewField = 'foo';

thanks for this post. I want to add something that can be useful.

For IE, it is good to use

object["property"] = value;

syntax because some special words in IE can give you an error.

An example:

object.class = 'value';

this fails in IE, because "class" is a special word. I spent several hours with this.

With ECMAScript since 2015 you can use Spread Syntax ( …three dots):

let  people = { id: 4 ,firstName: 'John'};
people = { ...people, secondName: 'Fogerty'};

It's allow you to add sub objects:

people = { ...people, city: { state: 'California' }};

the result would be:

{  
   "id": 4,
   "firstName": "John",
   "secondName": "Forget",
   "city": {  
      "state": "California"
   }
}

You also can merge objects:

var mergedObj = { ...obj1, ...obj2 };

You can also use Object.assign from ECMAScript 2015. It also allows you to add nested attributes at once. E.g.:

const myObject = {};

Object.assign(myObject, {
    firstNewAttribute: {
        nestedAttribute: 'woohoo!'
    }
});

Ps: This will not override the existing object with the assigned attributes. Instead they'll be added. However if you assign a value to an existing attribute then it would be overridden.