Trying to prevent duplicate users with same email address in my custom user table

[Thomas Miles]

I am writing a client script to stop a user from creating a new user record if the same address is in the system already

function onSubmit() {
    //Type appropriate comment here, and begin script below
    var currentEmail = g_form.getValue('email');
    
    var newUser = new GlideRecord('table_name');
    newUser.addQuery('email', currentEmail);
    newUser.query();
    if (newUser.next()) { 
        return false;
        
    }
}

[Community Alums]

yeah , you can still use this feature, it doesn't matter the scope of the app. 

Add unique field in the global for the table Dictionnary Entry [sys_dictionary] and after that switch to your scope to check the field Unique.