How to Show and Hide Tabs

// executionContext is passed as function parameter
var formContext = executionContext.getFormContext();

// Show tab
var detailsTab = formContext.ui.tabs.get("Details"); 
detailsTab.setVisible(true);

// Hide tab
var detailsTab = formContext.ui.tabs.get("Details"); 
detailsTab.setVisible(false);

Source: formContext.ui.tabs (Client API reference)