How to add the users entered in the user name field( peoplepicker) as site collection administrator in Sharepoint Online using JSOM

Using Javascript, in SPO I am trying to make a user entered via UI as a site collection administrator with the property set_isSiteAdmin(); but it is not working and trowing error function not exist. 

Below is the code I am using..

Can you someone please help me to fix this using JSOM in SPO.

function makeusersiteadmin() {


    var _peoplePicker = this.SPClientPeoplePicker.SPClientPeoplePickerDict.peoplePickerspanId_TopSpan;

    // Get information about users.
    var users = _peoplePicker.GetAllUserInfo();
    for (var i = 0; i < users.length; i++) {
        var user = users[i];
        var email = user.EntityData.Email;

    }


    var context = new SP.ClientContext.get_current();
    var web = context.get_web();
    this.user = web.get_siteUsers().getByEmail(email);
    user.set_isSiteAdmin();
    user.update();
    context.load(user);
    context.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));

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

Manoj Nagasarapu