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);

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.

It's a simple push object to array operation. Please try below

var data=[];

var i;
for (i = 0; i < clients.length; i++) { 
  data.push({
    date:clients.date,
    contact:clients.contact
  });
}

Simply do this :

Copyjsondata['FDamount'] = 'false';
jsondata['DDamount'] = 'true';

Or this :

Copyjsondata.FDamount = 'false';
jsondata.DDamount = 'true';

By the way, you define boolean as string, the correct way should be :

Copyjsondata['FDamount'] = false;
jsondata['DDamount'] = true;

To push a little bit further, you can use jQuery.extend to extend the original var, like this :

CopyjQuery.extend(jsondata, {'FDamount': 'false', 'DDamount': 'true'});
// Now, jsondata will be :
{"all":"true","FDamount":"false","DDamount":"true"}

jQuery.extend is available when using jQuery (of course), but I'm sure you can find similar methods in other libraries/frameworks.

(I'm using single quotes, but double quotes works too)