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

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

}

console.log(jsonObj);

There may be a better way to do this, but URLEncoding it seems to work.

Try this:

String jsonStr = '{"id":"0684D0000004VgeTTE","success":true,"errors":[]}';
String encoded = EncodingUtil.urlEncode(jsonStr, 'UTF-8');
String jsonStr2 = '{"description":"Some Text","machinename":"' + encoded + '","ipaddress":"192.128.0.0","version":"v3"}';

Map<String,Object> obj = (Map<String,    Object>)JSON.deserializeUntyped(jsonStr2);
System.debug(EncodingUtil.urlDecode((String)obj.get('machinename'), 'UTF-8'));

Of course it all depends what you are going to do with it on the other end, but this may be useful for you.

You probably want to use a JSON list instead of a dictionary as the toplevel element.

So, initialize the file with an empty list:

with open(DATA_FILENAME, mode='w', encoding='utf-8') as f:
    json.dump([], f)

Then, you can append new entries to this list:

with open(DATA_FILENAME, mode='w', encoding='utf-8') as feedsjson:
    entry = {'name': args.name, 'url': args.url}
    feeds.append(entry)
    json.dump(feeds, feedsjson)

Note that this will be slow to execute because you will rewrite the full contents of the file every time you call add. If you are calling it in a loop, consider adding all the feeds to a list in advance, then writing the list out in one go.

var Str_txt = '{"theTeam":[{"teamId":"1","status":"pending"},{"teamId":"2","status":"member"},{"teamId":"3","status":"member"}]}';

If you want to add at last position then use this:

var parse_obj = JSON.parse(Str_txt);
parse_obj['theTeam'].push({"teamId":"4","status":"pending"});
Str_txt = JSON.stringify(parse_obj);
Output //"{"theTeam":[{"teamId":"1","status":"pending"},{"teamId":"2","status":"member"},{"teamId":"3","status":"member"},{"teamId":"4","status":"pending"}]}"

If you want to add at first position then use the following code:

var parse_obj = JSON.parse(Str_txt);
parse_obj['theTeam'].unshift({"teamId":"4","status":"pending"});
Str_txt = JSON.stringify(parse_obj);
Output //"{"theTeam":[{"teamId":"4","status":"pending"},{"teamId":"1","status":"pending"},{"teamId":"2","status":"member"},{"teamId":"3","status":"member"}]}"

Anyone who wants to add at a certain position of an array try this:

parse_obj['theTeam'].splice(2, 0, {"teamId":"4","status":"pending"});
Output //"{"theTeam":[{"teamId":"1","status":"pending"},{"teamId":"2","status":"member"},{"teamId":"4","status":"pending"},{"teamId":"3","status":"member"}]}"

Above code block adds an element after the second element.