Add a SP User to a SP Group other than current user using CSOM or REST

Hi,

I want to add a SP User (from AD) to a SP Group other than current user using CSOM or REST.

Below code shows how to add current user to a SP Group (Link)

var user;
var visitorsGroup;

function runCode() {

     var clientContext = new SP.ClientContext();
     var groupCollection = clientContext.get_web().get_siteGroups();
     
     // Get the visitors group, assuming its ID is 23.
     visitorsGroup = groupCollection.getByName('Approvers');
     user = clientContext.get_web().get_currentUser();
     var userCollection = visitorsGroup.get_users();
     userCollection.addUser(user);

     clientContext.load(user);
     clientContext.load(visitorsGroup);
     clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded() {
    alert(user.get_title() + " added to group " + visitorsGroup.get_title());
}

function onQueryFailed(sender, args) {
    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

But i need to add a diff user which is not current user (say domain\login).

Please help

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